INDUSTRIAL    CHEMISTRY 

BEING    A    SERIES    OF    VOLUMES    GIVING 
A    COMPREHENSIVE    SURVEY    OF 

THE    CHEMICAL    INDUSTRIES 


INDUSTRIAL   CHEMISTRY 

BEING   A   SERIES   OF   VOLUMES   GIVING   A 
COMPREHENSIVE   SURVEY   OF 

THE    CHEMICAL    INDUSTRIES 

EDITED  BY  SAMUEL   RIDEAL,  D.Sc.  LOND,,  F.I.C. 

FELLOW  OF   UNIVERSITY  COLLEGE,    LONDON 
ASSISTED   BY 

JAMES  A.  AUDLEY,   B.Sc.,   F.I.C.  R.  S.  MORRELL,  M.A.,  PH.D. 

W.  BACON,  B.Sc.,  F.I.C.,  F.C.S.  J.  R.  PARTINGTON,  M.A.,  PH.D. 
E.DE  BARRY  BARNETT,  B.Sc.,  A. I.C.     ARTHUR  E.  PRATT,  B.Sc., Assoc.R.S.M. 

M.  BARROWCLIFF,  F.I.C.  ERIC  K.  RIDEAL,  M.A.,  PH.D.,  F.I.C. 

H.  GARNER  BENNETT,  M.Sc.  W.  H.  SIMMONS,  B.Sc.,  F.I.C. 

F.  H.  CARR,  F.I.C.  R.  W.  SINDALL,  F.C.S. 

S.  HOARE  COLLINS,  M.Sc.,  F.I.C.  HUGH  S.  TAYLOR,  D.Sc. 

H.  C.  GREENWOOD,  O.B.E.,  D.Sc.,  ARMAND  DE  WAELE,  B.Sc. 

F.I.C.  C.  M.  WHITTAKER,  B.Sc. 
&C.,  &c. 


INDUSTRIAL  GASES 


BY 

HAROLD    CECIL    GREENWOOD 

O.B.E.,  D.Sc.  (MANCHESTER),  F.I.C. 

SCIENTIFIC   ADVISER,    MUNITIONS   INVENTIONS   DEPARTMENT 
FORMERLY    BEYER   FELLOW   AND    1851    EXHIBITION   SCHOl  AR-,QV-  ,1    - 
THE   UNIVERSITY   OF    MANCHESTER 


NEW   YORK 
D,    VAN    NOSTRAND    COMPANY 

25    PARK    PLACE 
1919 


PRINTED   IN    GREAT   BRITAIN 


a 


GENERAL    PREFACE 

THE  rapid  development  of  Applied  Chemistry  in  recent  years 
has  brought  about  a  revolution  in  all  branches  of  technology. 
This  growth  has  been  accelerated  during  the  war,  and  the 
British  Empire  has  now  an  opportunity  of  increasing  its 
industrial  output  by  the  application  of  this  knowledge  to  the 
raw  materials  available  in  the  different  parts  of  the  world. 
The  subject  in  this  series  of  handbooks  will  be  treated  from 
the  chemical  rather  than  the  engineering  standpoint.  The 
industrial  aspect  will  also  be  more ,  prominent  than  that  of 
the  laboratory.  Each  volume  will  be  complete  in  itself,  and 
will  give  a  general  survey  of  the  industry,  showing  how 
chemical  principles  have  been  applied  and  have  affected 
manufacture.  The  influence  of  new  inventions  on  the 
development  of  the  industry  will  be  shown,  as  also  the 
effect  of  industrial  requirements  in  stimulating  invention. 
Historical  notes  will  be  a  feature  in  dealing  with  the 
different  branches  of  the  subject,  but  they  will  be  kept 
within  moderate  limits.  Present  tendencies  and  possible 
future  developments  will  have  attention,  and  some  space 
will  be  devoted  to  a  comparison  of  industrial  methods  and 
progress  in  the  chief  producing  countries.  There  will  be  a 
general  bibliography,  and  also  a  select  bibliography  to  follow 
each  section.  Statistical  information  will  only  be  introduced 
in  so  far  as  it  serves  to  illustrate  the  line  of  argument. 

Each  book  will  be    divided   into   sections   instead    of 
chapters,  and  the  sections  will  deal  with  separate  branches 
of  the  subject  in  the  manner  of  a  special  article  or  mono- 
graph.    An  attempt  will,  in  fact,  be  made  to  get  away  from 
A,  v  72 

458*793 


vi  GENERAL  PREFACE 

the  orthodox  textbook  manner,  not  only  to  make  the  treat- 
ment original,  but  also  to  appeal  to  the  very  large  class  of 
readers  already  possessing  good  textbooks,  of  which  there 
are  quite  sufficient.  The  books  should  also  be  found  useful 
by  men  of  affairs  having  no  special  technical  knowledge,  but 
who  may  require  from  time  to  time  to  refer  to  technical 
matters  in  a  book  of  moderate  compass,  with  references  to 
the  large  standard  works  for  fuller  details  on  special  points 
if  required. 

To  the  advanced  student  the  books  should  be  especially 
valuable.  His  mind  is  often  crammed  with  the  hard  facts 
and  details  of  his  subject  which  crowd  out  the  power  of 
realizing  the  industry  as  a  whole.  These  books  are  intended 
to  remedy  such  a  state  of  affairs.  While  recapitulating  the 
essential  basic  facts,  they  will  aim  at  presenting  the  reality 
of  the  living  industry.  It  has  long  been  a  drawback  of  our 
technical  education  that  the  college  graduate,  on  commencing 
his  industrial  career,  is  positively  handicapped  by  his 
academic  knowledge  because  of  his  lack  of  information  on 
current  industrial  conditions.  A  book  giving  a  compre- 
hensive survey  of  the  industry  can  be  of  very  material 
assistance  to  the  student  as  an  adjunct  to  his  ordinary  text- 
books, and  this  is  one  of  the  chief  objects  of  the  present 
series.  Those  actually  engaged  in  the  industry  who  have 
specialized  in  rather  narrow  limits  ^will  probably  find  these 
books  more  readable  than  the  larger  textbooks  when  they 
wish  to  refresh  their  memories  in  regard  to  branches  of  the 
subject  with  which  they  are  not  immediately  concerned. 

The  volume  will  also  serve  as  a  guide  to  the  standard 
literature  of  the  subject,  and  prove  of  value  to  the  con- 
sultant, so  that,  having  obtained  a  comprehensive  view  of 
the  whole  industry,  he  can  go  at  once  to  the  proper 
authorities  for  more  elaborate  information  on  special  points, 
and  thus  save  a  couple  of  days  spent  in  hunting  through  the 
libraries  of  scientific  societies. 

As  far  as  this  country  is  concerned,  it  is  believed  that 
the  general  scheme  of  this  series  of  handbooks  is  unique, 
and  it  is  confidently  hoped  that  it  will  supply  mental 


GENERAL  PREFACE  vii 

munitions  for  the  coming  industrial  war.  I  have  been 
fortunate  in  securing  writers  for  the  different  volumes  who 
are  specially  connected  with  the  several  departments  of 
Industrial  Chemistry,  and  trust  that  the  whole  series  will 
contribute  to  the  further  development  of  applied  chemistry 
throughout  the  Empire. 

SAMUEL   RIDEAI,. 


FOREWORD 

BY 

DR.   J.   A.   HARKER,   F.R.S. 

t 

IT  is  with  the  deepest  regret  that,  on  the  eve  of  publication 

of  this  book,  I  have  to  record  the  untimely  death  of  the 
author. 

For  the  past  three  years  Dr.  Greenwood  had  been  in 
charge  of  the  division  of  the  Research  Laboratory  of  the 
Ministry  of  Munitions  at  University  College,  dealing  with 
the  synthesis  of  ammonia  from  its  elements.  As  Director 
of  the  Laboratory,  I  have  come  into  close  contact  with  him 
for  more  than  three  years  past,  and  have  therefore  had  a 
unique  opportunity  of  forming  a  judgment  of  the  high  value 
of  the  work  he  has  accomplished.  It  is  undoubtedly  largely 
due  to  his  untiring  energy,  research  ability  and  wide  know- 
ledge, that  a  sure  foundation  has  been  laid  for  the  future 
development  of  the  synthetic  ammonia  industry  in  this 
country. 

Although  only  thirty-two  years  of  age,  he  had  lived  long 
enough  to  establish  a  scientific  record  of  which  a  man  of 
more  advanced  years  might  well  be  proud.  Among  the 
long  list  of  his  published  researches  may  be  cited  those  on 
the  reduction  of  refractory  oxides,  the  production  of  ferro 
alloys  and  the  determination  of  the  boiling-points  of  metals 
at  high  temperatures  and  under  varying  pressures.  All  these 
were  carried  out  at  Manchester  University.  As  1851 
Exhibition  Scholar  Greenwood  worked  ten  years  ago  under 
Professor  Haber  at  Karlsruhe  on  the  study  of  catalysts  for 
ammonia  synthesis. 


FOREWORD 

He  was  awarded  the  degree  of  D.Sc.  from  Manchester 
University  in  1912  at  the  early  age  of  twenty-five,  and  the 
Fellowship  of  the  Institute  of  Chemistry  in  1918,  and  the 
O.B.E.  in  the  present  year. 

The  contents  of  this  volume  testify  to  the  thoroughness 
of  his  knowledge  in  an  important  branch  of  modern  chemis- 
try, but  only  those  who  have  had  the  privilege  of  working 
with  him  can  fully  realize  the  great  loss  which  science  has 
suffered  by  the  sudden  termination  of  so  brilliant  a  career. 

J.  A.  HARKER. 

MINISTRY  OF  MUNITIONS, 
24,  OLD  QUEEN  STREET, 

LONDON,  S.W.  i. 

Novembei;   1919. 


AUTHOR'S    PREFACE 

THE  main  aims  of  this  book  on  Industrial  Gases  are  to  give 
a  general  account  of  the  manufacture  and  technical  manipu- 
lation of  gases,  to  describe  briefly  the  development  and 
general  principles  of  industrial  gas  technology  and  to  present 
a  collection  of  data  likely  to  be  useful  in  connection  with 
such  technology. 

Many  branches  of  gas  manufacture  are  still  in  course  of 
vigorous  development,  the  war  having  been  responsible  for 
much  progress,  e.g.  in  the  production  of  hydrogen,  for 
aeronautical  purposes  and  also  for  industrial  processes  such 
as  the  manufacture  of  synthetic  ammonia.  On  this  account 
it  is  difficult  to  give  in  all  cases  a  final  picture  of  the  subject, 
an  indication  of  the  present  trend  being  all  that  is  practicable. 

This  and  other  considerations  have  caused  me  to  con- 
centrate more  on  the  elucidation  of  general  principles  than 
on  very  detailed  treatment  of  the  various  processes  involved. 
Indeed,  the  latter  alternative  would  have  been  impracticable 
in  the  present  volume  on  account  of  the  enormous  field  to 
be  covered. 

Special  attention  has  been  paid  to  the  question  of  gaseous 
equilibria ;  the  ever-growing  importance  of  heterogeneous 
catalytic  gas  reactions  is  a  feature  of  the  present  situation. 

In  the  introductory  chapter  the  more  important  general 
considerations  relating  to  the  manufacture  and  use  of  gases 
are  briefly  discussed,  while  tables  of  reference  data  in  the 
form  required  for  immediate  use  in  technical  practice  are 
appended. 

From  this  book  have  been  excluded  certain  gases  such 
as  hydrogen  chloride,  chlorine,  ammonia,  etc.,  which  are 
treated  elsewhere  in  this  series.  In  view  of  the  dependence 
on  fuel  gases  of  most  of  the  important  industrial  gases  for 
their  manufacture  and  on  account  of  the  intimate  connection 
of  the  methods  of  production  of  fuel  gases  with  the  general 


x  AUTHOR'S   PREFACE 

question  of  industrial  gases,  a  concise  survey  of  the  manu- 
facture and  applications  of  gaseous  fuels  has  been  included. 
The  subject  is  not  treated  exhaustively  as  it  will  be  further 
elaborated  in  a  later  volume  of  this  series. 

Throughout  the  book  considerable  attention  has  been 
devoted  to  patents  where  such  patents  relate  to  differences 
in  principle  ;  although  much  of  the  subject-matter  of  patent 
literature  is  superficial  and  crude,  there  is  valuable  historical 
and  technical  information  to  be  obtained  from  the  same. 

A  word  may  be  said  here  with  regard  to  units.  While  the 
metric  system  has  many  undoubted  advantages  in  dealing 
with  gases  as  in  other  connections,  it  is  not  in  common  usage 
in  this  country  and  consequently  all  gases  have  been  con- 
sidered on  the  basis  of  1000  ft.3  at  15°  C.  under  a  pressure  of 
one  atmosphere.  As  regards  thermal  quantities,  since  all 
modern  chemical  works  now  use  the  Centigrade  thermometer, 
the  usual  B.T.U.  has  been  replaced  by  the  more  convenient 
C.H.U.  (Centigrade  Heat  Unit). 

Free  use  has  been  made  in  some  cases  of  many  excellent 
existing  textbooks,  from  which  matter  and  references  have 
been  drawn. 

Further,  I  desire  to  express  my  thanks  for  information 
received  from  various  sources,  especially  to  the  following  : 
Sir  George  Beilby,  Messrs.  A.  Boake,  Roberts  &  Co.,  I/td., 
Mr.  E.  M.  Boote,  Messrs.  The  Carbonic  Acid  Gas  Co., 
Messrs.  R.  &  J.  Dempster,  L/td.,  Dr.  R.  L,essing,  and  Dr. 
B.  B.  Maxted.  Assistance  was  also  given  by  the  late 
Thos.  Tyrer. 

Finally,  I  must  record  my  indebtedness  to  my  wife, 
Mary  G.  Greenwood,  B.Sc.,  for  her  constant  help  in  the 
collection  of  information  and  the  revision  of  the  MS. 


H.  C.  G. 


LONDON, 

October,  1919. 


CONTENTS 


PAGE 

GENERAL  PREFACE  .........  v 

AUTHOR'S  PREFACE  .........  ix 

CONTENTS   .....    ......  xi 

INTRODUCTION      ..........  ! 

Avogadro's  Hypothesis.  Laws  of  Gay  Lussac  and  Dalton.  Boyle's  Law. 
Law  of  Charles  and  Gay  Lussac.  Absolute  zero  of  temperature. 
Solution  :  Henry's  Law  ;  Dalton's  Law.  Sorption.  Diffusion.  Per- 
meability of  materials.  Critical  temperature  and  pressure.  Permanent 
gases  and  vapours.  Joule-Thomson  Effect.  Specific  heats  of  gases. 
Latent  heats  of  vaporisation  and  fusion.  .  Thermochemistry.  Thermo- 
dynamical  principles  governing  chemical  equilibria  in  the  gaseous  state  ; 
the  chemical  constant.  Velocity  of  reaction.  Heterogeneous  catalytic 
gas  reactions  :  reaction  velocity  ;  output  and  completeness.  Viscosity 
of  gases  :  stream-line  and  turbulent  motion.  Resistance  to  flow  of 
gases.  Influence  of  difference  in  level.  Physical  methods  of  testing 
the  purity  of  gases  :  gas  interferometer  ;  density  ;  effusion  ;  acoustical 
methods.  Separation  of  gaseous  mixtures.  Separation  of  liquid  or  solid 
particles  from  gases.  Methods  of  measuring  volumes  and  rates  of  flow 
of  gases.  Automatic  safety  and  purity  tests.  The  compression  of 
gases  :  work  of  compression  ;  adiabatic  compression  ;  isothermal  com- 
pression. Notes  on  compressed  gases  :  safety  precautions.  Liquefied 
gases.  Heat-interchange.  Desiccation  of  gases.  The  storage  of  gas. 
Reference  data.  References  ...  I 


PART    I. 

THE    GASES   OF   THE   ATMOSPHERE 
SECTION    L— AIR. 

Property  of  air.     Composition  of  the  atmosphere    .....       58 

The  liquefaction  of  the  permanent  gases  (air).  Theory  of  cooling  by  the 

Joule-Thomson  Effect :  expansion  at  — 100°  C. ;  the  case  of  hydrogen  .  60 

MANUFACTURE  OF  -JUo^uiD  AIR  :  Useful  constants.  Hampson  system. 

Linde  system  :  effect  of  pre-cooling.  Claude  system  ....  69 

Properties  of  liquid  air.  Applications  of  liquid  air.  Separation  of  the  con- 
stituents of  liquid  air  :  theoretical  considerations  ....  77 


xii  CONTENTS 

PAGE 

MANUFACTURE  OF  OXYGEN  AND  NITROGEN.     Linde  system :   Oxygen 
plants      Nitrogen  plants.    New  Linde  system.    Claude  system.    Pictet 
system  .  ........       81 

Separation  of  the  rare  gases   .........       92 

References   ............       92 


SECTION    II.— OXYGEN. 

Properties  of  oxygen      ..........  93 

MANUFACTURE : 

General    ........                   ...  94 

By  the  fractionation  of  liquid  air           .......  94 

By  electrolysis 94 

By  alternate  formation  and  decomposition  of  higher  oxides,  etc.       .          .  95 

By  auto-combustion  methods       ........  98 

By  the  action  of  water  on  peroxides  and  the  like    .....  98 

By  physical  methods  (in  the  gaseous  state)     ......  99 

Compression  of  oxygen  .         .         .          .          .         .         .          .         .100 

Comparison  of  costs  of  production  and  purity  attainable  by  different  processes  101 
Applications  of  oxygen :   scientific  and  laboratory  uses ;  therapeutic  uses  j 

welding  and  cutting  of  metals  ;  other  applications       ....  102 

Oxygen-enriched  air :  use  in  the  blast  furnace ;  use  in  the  arc  process  for 

nitrogen  fixation  ;  use  in  the  Hausser  process  ;  other  applications         .106 

Estimation  and  testing  of  oxygen    ........  108 

References  ............  109 


SECTION    III. —NITROGEN. 

Properties  of  nitrogen    ...  ......     1 10 

MANUFACTURE: 

General    ....  ...  .          .     in 

By  the  fractiouation  of  liquid  air 112 

By  direct  chemical  removal  of  the  oxygen  from  air  .  .  .  ."112 
From  producer  gas  and  products  of  combustion  .  .  .  .  .114 
By  physical  methods  (in  the  gaseous  state)  .  .  .  .  .  115 

By  direct  chemical  methods 1 16 

Purification  of  nitrogen :    from  carbon  monoxide ;    from  carbon  dioxide ; 

from  oxygen  j  from  sulphur  compounds     .         .         .         .         .          .116 

Comparison  of  costs  of  production  and  purity  attainable  by  the  different 

processes 117 

Applications    of    nitrogen — nitrogen    fixation :     cyanamide  process ;    the 
synthesis  of  ammonia ;  the  formation  of  metallic  nitrides  ;   the  direct 
production   of  cyanides ;     the   Hausser  process  ;    comparison  of  the 
power    requirements   in   various  nitrogen    fixation    processes ;     other 
applications  .         .         .          .         .          .          .          .         .         .         •     u/ 

Estimation  and  testing  of  nitrogen  .         .          .          .  .         .         .122 

References  .          .         .         .         .          .          .          .          .          .          .         .122 


CONTENTS  xiii 


• 


PAGE 


SECTION  IV.— THE  RARE  GASES  OF  THE 
ATMOSPHERE. 

General        ............     123 

History  of  the  discovery  of  the  rare  gases          .         .         .          .  .  .123 

ARGON.     Occurrence.     Manufacture.     Properties  and  applications  .  .124 

NEON.     Occurrence.     Isolation.     Properties  and  applications    .  .  .128 

HELIUM.     Occurrence.     Manufacture.     Properties  and  applications  .  .130 

KRYPTON  AND  XENON.     Occurrence.     Isolation  and  properties  .  .     132 

Niton           .         .         .          .         .          .          .          .          .          .  .  .      132 

References   .          .                   .          ...         .         .          .  .  .      133 


SECTION   V.— OZONE. 

Occurrence  ............     134 

Properties  of  ozone        .         .          .          .         .          .          .          .          .         -134 

Production  of  ozone:    general;  by  chemical  methods;  by  thermal  treat- 
ment of  oxygen  ;    by  electrolysis  ;    by  photochemical  means  j  by  the 
electric  discharge    .          .          .         .         .         .         .          .          .          .136 

MANUFACTURE  :  general  principles  of  ozonizers  :   influence  of  the  character 
of  the  discharge ;    influence  of  dielectrics  ;    relation  between  energy, 
concentration   and   production ;    influence  of  moisture ;    influence   of 
temperature  ;  materials  of  construction.     Construction  and  production 
of  the  various  commercial  types  of  ozonizers       .          .         .         .         .140 

Applications   of  ozone :    water  sterilization  ;    air  purification  ;     chemical 

applications  ;  other  applications 145 

Detection  and  estimation  of  ozone  ........     149 

References  ............      150 


PART   II. 

HYDROGEN,  CARBON  MONOXIDE, 
CARBON  DIOXIDE,  SULPHUR  DI- 
OXIDE, NITROUS  OXIDE,  ASPHYX- 
IATING GASES. 

SECTION   VI.— HYDROGEN.     STATIONARY 
PLANTS. 

Occurrence  ............  152 

Physical  properties.     Liquid  hydrogen  ;  properties.     Chemical  properties  .  152 
MANUFACTURE  (STATIONARY  PLANTS): 

General          ...........  155 

From  water  gas— replacement  of  carbon  monoxide  by  hydrogen  .          .  156 
B.A.M.A.G.  continuous  catalytic  process  :  theory  of  the  B.A.M.A.G. 

continuous  catalytic  process   .         .          .          .         .         .  159 

Griesheim-Elektron  process :  theory  of  the  Griesheim-FJektron  process  164 


xiv  CONTENTS 

MANUFACTURE  (STATIONARY  PLANTS)  : — continued.  PAGE 

From  water  gas — by  liquefaction  of  the  carbon  monoxide  :  the  Linde- 

Frank-Caro  process 168 

By  the  action  of  water  or  steam  on  iron  or  carbon      .         .         .         .174 

General      .         .         .         .         .         .         .         .         .         .         .174 

Iron  oxide  processes :   Lane  process ;  Messerschmitt  process ;  pro- 
cess of  the  Internationale  Wasserstoff  A.G. ;  Strache  process         .     175 
Dieffenbach  and  Moldenhauer  process   .         .          .         .         .          .185 

Bergius  process 187 

By  the  decomposition  of  hydrocarbons  :  Carbonium  Gesellschaft  pro- 
cess ;     Rincker    and    Wolter    process  ;    Oechelhauser    process ; 

B.  A.M.  A.G.  (Bunte)  process 189 

By  electrolysis        .          .         .         .         .         .         .         .         .  194 

General.    Principal  electrolytic  processes  used  in  practice  :  Schuckert 
process  ;  Schmidt  process  ;  Garuti  process  ;  Schoop  process  ;  Inter- 
national Oxygen  Co.'s  processes  ;  other  processes.     Danger  limits 
as   regards   intermixing   in    electrolytic    hydrogen    and    oxycen. 
Hydrogen  as  a  by-product          .         .         .         .         .         .  194 

Other  processes  for  the  manufacture  of  hydrogen         ....     203 

By  the  action  of  acids  or  alkalis  on  metals 203 

Separation  from  water  gas  and  the  like  by  physical  methods     .         .     204 
Through  the  intermediary  of  formates    ......     205 

Miscellaneous  methods          ........     205 

Production  of  a  mixture  of  nitrogen  and  hydrogen  for  use  in  synthetic 

ammonia  manufacture        .......         »     207 

Methods  of  final  purification  of  hydrogen.     From  carbon  monoxide :   by 

soda-lime ;    by  caustic  soda  solution  ;    by  cuprous  chloride  solution  ; 

by   conversion  into  methane ;     by  calcium  carbide.      From    carbon 

dioxide.     From  sulphur  compounds.     From  other  impurities       .         .     207 

Comparison  of  costs  of  production  and  purity  attainable  by  the  different 

methods 212 

Applications  of  hydrogen  :   hydrogenation  of  oils  and  fats  ;  manufacture  of 

synthetic  ammonia ;  other  applications     .         .         .         .         .         .213 

References  .  .         .     221 


SECTION  VII.— THE  PRODUCTION  OF  HYDROGEN 
FOR  MILITARY  PURPOSES. 

Field  processes .     223 

Portable  apparatus  for  use  in  the  field      .......     224 

Silicon  and   "Silicol"  processes:    the  Schuckert  process;    the  Silicol 

process -  224 

Hydrogenite  process  ........  .227 

Hydrolith  process •     228 

By  the  action  of  acids  and  alkalis  on  metals :  action  of  sulphuric  acid 
on  iron  or  zinc ;    action  of  caustic  soda  on  aluminium  ;    action  of 

activated  aluminium  on  water 229 

Other  processes          .         .         .         .         •         •         •         •         •         -231 


CONTENTS  xv 

PAGE 

Adaptations  of  stationary  types  of  plant  to  field  purposes  ....  232 

Semi-portable  plant       ..........  232 

Stationary  plants            ..........  233 

General :   Lifting  power  of  the  hydrogen  ;  effect  on  fabrics ;   costs  by  the 

different  processes  ..........  233 

Estimation  and  testing  of  hydrogen          .......  235 

References 236 


SECTION   VIIL— CARBON   MONOXIDE. 

Properties  of  carbon  monoxide        ........     237 

MANUFACTURE  : 

Applications  of  carbon  monoxide :  general ;  the  Mond  nickel  process — 
metallic  carbonyls — the  refining  of  nickel  by  the  Mond  process ;  the 
production  of  formates,  oxalates  and  acetates  j  the  production  of  gases 
rich  in  methane ;  the  manufacture  of  phosgene— properties  and  uses 
of  phosgene ;  other  applications  .  .  .  .  .  .  .241 

Estimation  of  carbon  monoxide       .         .         .         .         .         .         .         .     254 


SECTION   IX.— CARBON   DIOXIDE. 

Occurrence  ............  256 

Properties  of  carbon  dioxide  ;   liquid  carbon  dioxide  j  solid  carbon  dioxide  256 
MANUFACTURE  : 

General         ....                   259 

Generation  of  pure  carbon  dioxide    .                                      .                   .  259 

Utilization  of  natural  sources         .                            ....  259 

By  the  thermal  decomposition  of  carbonates  .                  ...  260 

By  the  action  of  acids  on  carbonates       ...                             .  261 

Production  as  a  by-product  in  fermentation  processes       .         .         .  262 

By  other  methods .  262 

Concentration  of  carbon  dioxide  from  mixtures  with  other  gases            .  263 

By  means  of  water  under  pressure           ......  263 

By  the  alternate  formation  and  decomposition  of  alkali  bicarbonates 

in  solution   ..........  264 

By  liquefaction    .                                                .                   ...  264 

Production  and  concentration  of  dilute  carbon  dioxide  from  products 

of  combustion  j  Siirth  system           .                             ...  264 

Production  and  concentration  of  dilute  carbon  dioxide  from  lime-kiln 

gases  ...........  267 

The  production  and  transport  of  liquid  carbon  dioxide       ....  268 

The  production  and  transport  of  solid  carbon  dioxide         .                             .  268 
Applications  of  carbon  dioxide :  in  the  Solvay  ammonia  soda  and  the  Glaus- 
Chance  sulphur  recovery  processes;   in  the  manufacture  of  artificial 

mineral  waters ;  in  refrigeration  plant ;  other  applications   .          .          .  269 

Estimation  and  testing  of  carbon  dioxide           .                             .                   •  272 

References  .         .                   273 


xvi  CONTENTS 

SECTION  X.— SULPHUR   DIOXIDE. 

PAGE 

Properties  of  sulphur  dioxide           ........  274 

MANUFACTURE : 

General    ... 275 

Production  of  dilute  sulphur  dioxide    .         .         ..          .         .         .         .277 

Concentration  of  dilute  sulphur  dioxide  :  the  Hanisch  and  Schroder  process  278 

Transport  of  liquid  sulphur  dioxide 279 

Applications  of  sulphur  dioxide  :   manufacture  of  sulphuric  acid,  sulphuric 
anhydride  and   sodium   sulphate  j     manufacture   of  wood  pulp ;     in 
refrigeration    plant ;    as  a   solvent  j    for  bleaching  purposes ;    as  a 

disinfectant ;  other  applications        .         .         .         .         .                  .  280 

The  estimation  and  testing  of  sulphur  dioxide  ......  283 

References 284 


SECTION  XL— NITROUS   OXIDE. 

Properties  of  nitrous  oxide 285 

MANUFACTURE.     From  ammonium  nitrate  ;  by  other  methods  .  286 

Purification 288 

Applications  of  nitrous  oxide  ........  288 


SECTION  XII.— ASPHYXIATING   GASES. 

Introduction          .......  ...     291 

The  development  of  gas  warfare ,291 


PART   III. 

GASEOUS    FUELS. 
SECTION   XIII. 

General  considerations  .         .         .         .         .         .         .         .  295 

Fundamental  principles  relating   to   the  use  of  gaseous  fuels  :    table  of 

constants ;  calorific  value ;    the  mechanism  of  flame  ;    calorific  value 

of  technical  air-gas  mixtures ;   ignition  temperature  ;  explosive  limits 

and  the  velocity  of  propagation  of  explosion 296 

Fundamental  principles  of  the  production  of  gaseous  fuels  of  low  calorific 

value  :   action  of  air  on  carbon  ;  action  of  steam  on  carbon ;   action 
~^f  a  mixture  of  air  and  steam  on  carbon  ;  action  of  carbon  dioxide  on 

carbon  ...........     301 

TECHNICAL    PRODUCTION    OF   GASEOUS    FUELS    OF    Low    CALORIFIC 

VALUE  : 
Air  producer  gas        ..........     313 

General.     General  principles  of  operation  j  applications      .         .         .     313 


CONTENTS  xvii 

PAGE 

Water  gas 316 

General.     General  principles  of  operation           .         .          .         .         .  316 

Blue  water  gas  plants ;    the   Lowe  system  of  operation ;    Dellwik- 

Fleischer  system  ;  Kramer  and  A  arts  process       .          .         .          .318 

Carburetted  water  gas     .........  322 

Applications  of  blue  water  gas          .......  325 

Semi-water  gas           .......          ...  325 

General.  General  principles  of  operation.  Choice  of  fuel :  nitrogen 
content  of  coal  ;  sulphur  "content  of  coal ;  other  deleterious  con- 
stituents of  coal.  The  saturation  temperature  of  the  blast.  The 

rate  of  gasification .         .         .  325 

Semi-water  gas  plants :   general  ;   pressure  plants  ;   ammonia  recovery 

and  cleaning  of  semi-water  gas  .......  335 

Mond  process         .         ,         .         .                  .         .         .         .         .  339 

Use  of  semi- water  gas  for  furnace  operations      .....  340 

The  production  of  power  by  the  combustion  of  semi-water  gas  in  gas 
engines  :  general ;  plants  for  power  production  ;  suction  plants ; 
use  of  suction  gas  in  internal  combustion  engines          .         .         -341 

Coal  gas  as  a  fuel       ..........  347 

General         .         .         .         .         .         .         .         .         .         .         .  348 

Applications  of  coal  gas  :  furnace  operations;  power  production;  other 

applications     ..........  348 

Coke-oven  gas .         .         .         .         .         .         .         .         .         .         .  352 

Blast-furnace  gas ...  353 

Natural  gas .          .          .         .         .  354 

Surface  combustion  .         .         .         ...         .         .                  .  355 

Gas  calorimetry          .         .          .          .         ...          .          .         .          .  357 

References .         .         .         .         .  358 

INDEX  OF  SUBJECTS 359 

INDEX  OF  NAMES  OF  AUTHORS        .         .         .         .         .         .365 


ERRATA 

Page  144,  line  25,  for  7000  to  9000  volts  rtad  4000  volts. 
Page  273,  References,  for  Goosman  read  Goosmann. 


INDUSTRIAL  GASES 


INTRODUCTION 

THE  object  of  this  introductory  chapter  is  to  outline  and 
emphasize  some  of  the  more  important  fundamental  physical 
and  physico-chemical  principles  forming  the  basis  of 
technical  gas  reactions.  In  no  branch  of  modern  chemistry 
is  the  importance  of  a  knowledge  of  the  development  of 
physical  chemistry  more  important  than  in  the  study  of 
reactions  and  phenomena  of  the  gaseous  state  of  matter. 
This  is  largely  to  be  attributed  to  the  greater  ease  of  appli- 
cation of  generalizations  to  the  gaseous  state,  owing  to  its 
simple  physical  condition  as  compared  with  the  liquid  and 
solid  states.  It  is  to  be  feared  that  many  technical  gas 
processes  have  been  worked  without  due  appreciation  of 
the  thermodynamical  principles  determining  their  success 
or  failure.  A  most  vital  factor  contributing  to  this  state 
of  affairs  is  the  fact  that  in  many  cases,  e.g.  in  the  coal-gas 
industry,  the  responsibility  and  control  are  delegated  to 
engineers  and  not  to  chemists;  at  the  same  time,  the 
engineering  aspects  of  the  operations  must  receive  careful 
consideration. 

No  attempt  will  be  made  in  the  present  volume  to  give 
a  detailed  theoretical  treatment  of  the  various  physico- 
chemical  generalizations  and  data  to  which  reference  is 
made ;  for  such  information,  works  on  physical  chemistry, 
etc.,  must  be  consulted.  The  intention  is  rather  to  draw 
attention  to  the  salient  points  of  importance  in  the  investi- 
gation and  control  of  technical  operations  relating  to  the 
manufacture  or  utilization  of  gases. 

Avogadro's    Hypothesis. — This   generalization  states 

A.  I 


/?*•'.  :•/;•"•*:  j  :  .^[INDUSTRIAL  GASES 

that  equal  volumes  of  different  gases  contain  equal  numbers 
of  molecules  under  similar  conditions  of  temperature  and 
pressure.  As  a  practical  consequence  of  this  law,  it  may  be 
stated  that,  to  a  fairly  close  approximation,  the  molecular 
weight  in  grams  of  any  permanent  gas,  i.e.  a  substance 
above  its  critical  temperature,  at  o°  C.  and  760  mm.,  occupies 
22*38  litres.  The  volume  at  15°  C.  will  consequently  be — 

22-38  X  288  v 

— litres  =  23-61  litres. 

273 

A  useful  figure  is  the  corresponding  volume  of  a  pound 
molecule,  which  is  equal  to — 

358-5  ft. 3  at  o°  C. 
or      378-2  ft.  3  at  15°  C. 

With  vapours,  i.e.  gases  below  their  critical  temperatures, 
the  volume  is  usually  slightly  lower,  e.g.  22*26  litres  at  o°  C. 
and  760  mm.  in  the  case  of  carbon  dioxide. 

Laws  of  Gay  Lussac  and  Dalton. — According  to  these 
well-known  generalizations,  chemical  combination  between 
gases  takes  place  in  definite  proportions  and  the  volume 
of  the  product  or  products  bears  a  simple  relation  to 
the  volumes  of  the  reactants,  under  like  conditions  of 
temperature  and  pressure.  This,  of  course,  is  intimately 
connected  with  Avogadro's  Hypothesis. 

Boyle 's  Law.    Law  of  Charles  and  Gay  Lussac.— 
Boyle's  Law  states   that  pv  =  a  constant,  where  p  and  v 
represent  the  pressure  and  volume  of  a  given  mass  of  gas,  the 
temperature  being  maintained  constant. 

The  Law  of  Charles  and  Gay  Lussac  enunciates  that  the 
effect  of  variation  of  temperature  under  constant  pressure 
is  to  vary  the  volume  in  direct  proportion  to  the  (absolute) 
temperature  variation,  or,  conversely,  if  the  volume  be  kept 
constant,  that  the  pressure  varies  as  the  absolute  temperature. 
The  combined  result  of  these  generalizations  may  be 
expressed  thus — 

i>v 

Z—     —  a  constant  (K) 

or    pv  =  KT. 


INTRODUCTION 


When  pv  refers  to  one  gram  molecule  at  N.*T.P.,  the 
equation  is  usually  written  pv  =>  RT,  R  being  termed  the 
gas  constant  and  having  a  numerical  value  of  1*98  calories. 
Since  gram  molecules  are  inconvenient  units  for  industrial 
use,  the  more  general  form  will  be  adopted. 

This  relation,  however,  is  only  approximately  correct, 
particularly  as  regards  the  constancy  of  the  product  pv, 
as  even  the  permanent  gases  are  not  "  perfect  "  ;  vapours 
show  very  considerable  divergencies.  Due  recognition  of 
this  fact  is  of  importance  in  dealing  with  compressed  gases, 
and  the  extent  of  the  deviation  from  perfection  for  different 
gases  will  be  found  in  Table  12  (A),  under  the  heading  of  ft.3 
of  free  gas  contained  in  a  cylinder  of  i  ft.3  capacity  at  a 
pressure  of  120  atmospheres,  121  atms.  absolute.  The 
values  are  obtained  as  follows  : — e.g.,  in  the  case  of  hydrogen, 
the  variation  of  the  product  pv  with  v  at  a  temperature 

of  15-5°  C.  is— 

TABLE   i. 

AMAGAT.  COMPRESSIBILITY  OF  HYDROGEN. 


p  (atmospheres  absolute) 

t>v  . 

i 

I 

50 
1*0340 

100 

1-0689 

150 

I'lOII 

2OO 
1*1342 

•blbv 

i 

4.8-36 

Q3'^6 

136*23 

176*  34 

(cf.  Amagat,  Annales  de  Chim.  et  de  Phys.,  [6],  29,  (1883),  68). 
The  ratio    ~-    represents   the  ratio  of  the  mass  of  gas 

(or  the  volume  of  free  gas)  contained  in  a  given  reservoir 
at  the  particular  absolute  pressure  to  that  at  one  atmosphere 
absolute  pressure,  assuming  no  change  in  the  volume  of 
the  container.  The  curves  in  Fig.  i  give  the  variation  of 
pv  with  p  for  a  number  of  permanent  gases.  Most  of  the 
values  are  taken  from  Amagat's  investigations  (Annales  de 
Chim.  et  de  Phys.,  [5],  19,  (1880),  345  ;  [5],  22,  (1881),  353  ; 
[6],  29,  (1883),  68,  505)  and  have  been  arranged  in  all  cases 
so  that  the  product  pv  equals  unity  at  o°  C.  at  atmospheric 
pressure ;  at  the  particular  temperature  of  the  determination 
the  product  is  greater  in  accordance  with  the  coefficient  of 
expansion  of  the  gas  in  question.  In  the  case  of  oxygen, 


4  INDUSTRIAL   GASES 

1-20 


0-80 

50  IOO  ISO  2OO 

PRESSURE  ATMOSPHERES  (ABSOLUTE) 
FIG.  i. — Compressibility  of  Gases  at  the  ordinaryvTemperature. 


INTRODUCTION  5 

only  three  points  are  available,  namely,  i,  100,  and  200  atms., 
consequently  the  intermediate  points  of  the  curve  are  a 
little  uncertain. 

The  capacity    of    a   given    cylinder    at    the    (absolute) 


225 


200 


HYDROGEN 


175 


800 


25  50  75  100  125  150 

PRESSURE  ATMOSPHERES  (ABSOLUTE) 

FIG.  2. — Capacity  of  Cylinder  for  Compressed  Gases. 

pressure  px  can  readily  be  determined  from  these  curves  by 
evaluating  the  expression — 


where  (^w)!  and  (pv)x  represent  the  values  at  the  pressures 
of  one  and  px  atmospheres  respectively.  Curves  on  this 
basis  have  been  plotted  in  Fig.  2,  the  ordinates  representing 
the  volumes  of  free  gas  contained  in  a  given  cylinder  at  the 
pressures  denoted  by  the  abscissae. 


INDUSTRIAL  GASES 


This  variation  in  the  value  of  pv  is  due  to  the  joint 
action  of  two  opposing  factors :  (i)  the  attraction  between 
the  molecules,  acting  in  the  direction  of  lowering  the 
product  pv,  and  (2)  the  departure  from  perfect  compres- 
sibility owing  to  the  actual  dimensions  of  the  molecules, 
operative  in  the  opposite  direction.  Thus,  nitrogen  at  first 
shows  a  decrease  in  the  product  pv  with  rising  pressure 
and  subsequently  an  increase.  In  order  to  allow  for  the 
very  considerable  divergence  from  Boyle's  I,aw,  even  at 
moderate  pressures,  of  gases  such  as  carbon  dioxide,  various 
more  complete  equations  have  been  proposed.  The  growing 
imperfection  of  air  as  the  temperature  is  lowered  is  well 
shown  by  the  measurements  of  Witkowski  (Phil.  Mag.,  [5], 
41,  (1896),  288),  given  in  Table  2.  The  values  are  taken  so 
that  pv  =  i *ooo  at  N.T.P.,  as  in  Fig.  i. 

TABLE   2. 
WITKOWSKI.     COMPRESSIBILITY  OF  AIR. 


Pres- 
sure 

atras. 

Temperatures  °C. 

+  100 

+  16 

o 

-35 

-78-5 

-103-5 

-130 

-135 

-140 

-145 

I 

1-367 

1-0587 

I'OOOO 

0-8716 

0-7II9 

0-6202 

0-5229 

0-5046 

0-4862 

0-4679 

10 

1-3678 

I-0550 

0-9951 

— 



— 

— 

— 

— 

15 

1-3685 

•0529 

•9923 

— 



— 

— 

— 

"4°95 

•3786 

20 
25 

1-3691 
1-3698 

-0509 
•0488 

-9897 
•9869 

— 

•6778 
•6689 

•5697!    H4IO 
'5559  |    '4l83 

___ 

•3808 
•3476 

"3447 
•30i5 

30 

i'37°4 

•0468 

•9842 

— 

•6599 

'54*7 

•3936 

•3502 

•3063 

•2444* 

35 

I-37I3 

•0449 

•9816 

— 

•65IO 

•5270 

•3650 

•3115 

•2419 

40 

I-3725 

•°433 

•9793 

— 

•6423 

-5125 

-3329 

•2598 

•1128 

45 

I-3738 

•0419 

•9772 

—    - 

-6335 

•4980 

•2963 

•1942 

50 

1*3754 

•0408 

"9754 

•8288 

•6252 

•4839 

•2544 

•1605 

55 

I-377° 

•0399 

•9738 

•8253 

•6170 

•4701 

•2171 

•1553 

60 

1-3784 

•0390 

•9723 

•8219 

•6089 

•4567 

•2013 

•1556 

65 

1-3802 

•0384 

•9710 

•8187 

•6011 

'4439 

•1985 

•1576 

70 

1-3821 

•0381 

•9701 

•8158 

'5937 

•43i8 

•1989 

75 

1-3842 

•0379 

•9694 

•8132 

•5863 

•4206 

•2013 

80 

1-3866 

•0379 

•9688 

•8105 

-5796 

•4103 

•2043 

85 

1-3887 

•0380 

•9684 

•8o8l 

"5734 

•4014 

90 

1-3908 

•0382 

•9681 

•8058 

•5680 

•3948 

95 

1-3929 

•0386 

•9680 

•8038 

-5634 

•3903 

IOO 

i'395i 

•0390 

•9681 

•8023 

•5600 

•3881 

i°5 

!-3977 

-0397 

•9685 

•8013 

•5568 

•3874 

no 

1-4004 

•0406 

•9690 

•8006 

'5544 

•3877 

"5 

i"4°34 

•0418 

•9699 

•8004 

•5530 

•3892 

I2O 

1-4065 

•0432 

•9710 

•8006 

•5520 

•3914 

125 

-0448 

•9722 

•8012 

•5520 

•3944 

I30 

•0467 

•9738 

MM 

•5528 

•398i 

*  Corresponds  to  29  atms. 


INTRODUCTION 
In  the  more  complete  equation  of  Van  der  Waak  — 


the  quotient  of  the  constant  a  divided  by  v2  representing 
the  cohesion  effect,  and  b,  another  constant,  representing  the 
actual  dimensions  of  the  molecules,  the  constants  may  be 
evaluated  by  the  following  expressions  :— 


6-|£  =  approximately^ 

where 

Tc  and  pc  are  the  critical  temperature  and  pressure, 
p0  and  v0  represent  the  pressure  and  volume  of  the 
gas  at  the  absolute  temperature  T0, 

and      K  is  a  constant. 

The  value  of  this  equation  in  correlating  the  very 
different  behaviour  of  various  gases  under  varying  conditions 
of  temperature  and  pressure  is  well  seen  if  the  equation  is 
written  in  the  following  form,  substituting  the  above  values 
for  a  and  b  — 


where  TT,  <f>  and  6  represent  the  multiples  or  submultiples 
of  the  critical  values,  pressure,  volume*  and  temperature, 
respectively.  If,  now,  we  plot  TT<£  curves  instead  of  pv 
curves  we  obtain  practically  identical  curves  for  all  gases  ; 
for  equal  values  of  TT,  ^  and  6  two  gases  are  said  to  be  in 
corresponding  states. 

This  and  other  equations,  e.g.  that  of  Dieterici,  give  closer 
but  still  incomplete  agreement  with  experimental  results. 

Absolute    Zero   of   Temperature.  —  According  to  the 
L,aw  of  Gay  L,ussac  and  Dalton,  which  may  be  expressed  — 

KT 


*  The  critical  volume  of  the  mass  of  gas  under  consideration  is  the 
volume  at  the  critical  temperature  and  pressure. 


8  INDUSTRIAL   GASES 

the  volume  of  a  gas  should  become  equal  to  zero  when 
T=.o. 

The  observed  coefficient  of  expansion  of  gases,  i.e.  about 
^fj  of  the  volume  at  o°  C.  per  °  C.,  indicates  that  the 
absolute  zero  of  temperature,  i.e.  the  temperature  at  which 
the  molecules  have  ceased  to  have  relative  motion,  is 
approximately  273°  C.  below  the  freezing  point  of  water. 
More  exact  computations,  e.g.  from  the  Joule-Thomson 
effect  (see  below),  indicate  a  probable  value  of  —273-13°  C. 

Solution:  Henry 's  Law;  Dalton's  Law. — It  was 
shown  by  Henry  that  the  solubility  of  a  gas  is  proportional 
to  its  pressure,  and  by  Dalton,  shortly  afterwards,  that  with 
gaseous  mixtures  the  solubility  of  each  constituent  in  a 
liquid  is  proportional  to  the  partial  pressure  of  the  con- 
stituent, the  other  gases  behaving  as  a  vacuum.  I4ke 
many  other  "laws,"  these  generalizations  are  only  approxi- 
mately correct,  especially  for  a  gas  with  a  high  degree  of 
solubility. 

The  principle  of  partial  pressures  applies  to  man}- 
processes  besides  that  of  solution,  e.g.  the  temperature  at 
which  a  particular  constituent  of  a  gaseous  mixture  will 
liquefy  out  as  the  temperature  is  progressively  lowered  is 
dependent  on  its  partial  pressure.  Generally  speaking,  it 
may  be  stated  that  the  solubility  of  gases  in  water  falls  off 
as  the  temperature  is  raised  ;  with  other  solvents,  however, 
this  is  not  always  the  case. 

Sorption. — When  gases  are  taken  up  by  solids,  the 
phenomena  are  much  less  simple.  It  becomes  necessary 
to  differentiate  between  absorption,  i.e.  solution  or  uniform 
distribution  throughout  the  structure  of  the  solid,  and 
adsorption,  which  is  essentially  a  surface  condensation. 
The  combined  effect  is  sometimes  termed  sorption.  Thus, 
when  hydrogen  is  brought  into  contact  with  charcoal  at 
liquid-air  temperatures,  there  is  a  rapid  fall  in  pressure 
occupying  only  a  few  minutes,  attributed  to  adsorption, 
followed  by  a  slow  fall  over  several  hours,  considered  by 
McBain  (Z.  physik.  Chem.,  68,  (1909),  471)  to  be  a  slow 
penetration  into  the  structure  of  the  charcoal.  Similar 


INTRODUCTION  9 

effects  were  observed  by  Richardson  (/.  Amer.  Ctyem.  Soc., 
39,  (1917),  1828)  in  the  sorption  of  carbon  dioxide  and 
ammonia  by  charcoal.  In  some  cases  there  is  evidence  of 
the  formation  of  a  chemical  compound,  e.g.  with  oxygen 
and  charcoal  (Rhead  and  Wheeler,  Chem.  Soc.  Trans., 
(1913),  641).  In  adsorption  phenomena,  the  relation 
between  pressure  and  the^  extent  to  which  the  gas  is  taken 
up  is  much  more  complex  than  in  ordinary  solubility. 

Gases  are  taken  up  in  appreciable  quantities  by  many 
metals,  in  the  solid  and  especially  in  the  liquid  state,  the 
sorption  usually  increasing  with  the  temperature ;  at  the 
fusion  point  there  is  a  sudden  increase  in  the  sorption  in 
the  case  of  most  metals.  Thus,  metallic  iron  takes  up 
0-000035%  by  weight  of  hydrogen  at  416°  C.  and  0*000108% 
at  1450°  C.  (Jurisch,  Stahl  und-Eisen,  34,  (1914),  252). 
Between  23  and  750  mm.  the  weight  of  hydrogen  absorbed 
varies  as  the  square  root  of  the  pressure  for  a  given  allotropic 
modification  of  the  iron.  With  nitrogen,  the  sorption  by 
weight  is  0-00158%  at  878°  C.,  0-02103%  at  981°  C.,  falling 
off  to  0-01885%  at  1136°  C.,  the  amount  varying  as  the 
square  root  of  the  pressure  (Jurisch,  I.e.}. 

Diffusion. — The  diffusion  of  one  gas  into  another  takes 
place  with  considerable  rapidity  under  ordinary  conditions. 
The  rate  is  inversely  proportional  to  the  total  pressure  of 
the  two  gases,  and  approximately  proportional  to  the 
square  root  of  the  absolute  temperature.  The  effect  of 
increased  pressure  is  very  noticeable  if  a  mixture  of  two 
gases,  e.g.  nitrogen  and  hydrogen,  be  made  by  successive 
compression  of  the  two  gases  into  a  cylinder,  particularly 
if  the  cylinder  be  in  a  vertical  position,  and  the  lighter  gas 
be  introduced  second.  If,  however,  the  cylinder  be  disposed 
in  a  horizontal  position,  diffusion  is  almost  complete  on 
standing  12  to  24  hours. 

It  is  interesting  to  note  that  diffusion  is  scarcely  affected 
by  the  presence  of  a  perforated  partition,  although  the 
aggregate  area  of  communication  may  be  greatly  reduced. 

Permeability  of  Materials. — A  point  of  some  practical 
importance,  in  dealing  with  gases,  is  the  permeability  of 


10 


INDUSTRIAL   GASES 


materials.  Thus,  hydrogen  diffuses  through  heated  palla- 
dium or  platinum  and  to  a  lesser  degree  through  heated 
iron.  Quartz  is  appreciably  permeable  to  hydrogen  above 
1000°  C.,  while  indiarubber  is  fairly  permeable  to  gases. 
According  to  Dewar  (Proc.  Roy.  Institution,  21,  (1918), 
813)  the  rate  of  diffusion  of  various  gases  at  15°  C.  and 
760  mm.  pressure  through  a  rubber  membrane  of  0*01  mm. 
thickness  is  as  follows  : — 

TABLE   3. 
RATES  OF  DIFFUSION  THROUGH  RUBBER. 


Gas. 

Air 

Nitro- 

Carbon 

Helium 

Argon 

Oxy- 

Hydro- 

Carbon 

gen 

monoxide 

gen 

gen 

dioxide 

Rate  of  diffusion 

cm.3/cm.2/diem. 

2'0 

1-38 

1-88 

3'5 

2-56 

4-0 

II'2 

28-0 

The  rate  of  diffusion  increases  rapidly  with  temperature 
but  does  not  appear  to  be  directly  related  to  any  chemical 
or  physical  property  of  the  different  gases.  When  dealing 
with  mixtures  of  gases,  it  is  obvious  that  the  effect  of 
such  diffusion  will  be  to  produce  a  change  in  composition. 

Critical  Temperature  and  Pressure. — Permanent  Gases 
and  Vapours. — It  was  found  by  Andrews  that  for  each  gas 
there  is  a  certain  temperature  above  which  it  is  impossible 
to  effect  liquefaction  by  simple  compression,  however  great. 
This  temperature  is  termed  the  critical  temperature,  and 
the  pressure  of  the  system  at  this  point,  i.e.  the  pressure 
required  to  effect  liquefaction  at  the  critical  temperature, 
is  termed  the  critical  pressure.  The  values  of  the  critical 
pressures  are  comparatively  low  and  fall  off  as  the  value 
of  the  critical  temperature  decreases ;  thus,  for  hydrogen, 
the  critical  pressure  is  only  about  n  atmospheres. 

Joule-Thomson  Effect. — If  a  compressed  gas  be  allowed 
to  expand  to  a  lower  pressure  through  an  orifice  without 
the  production  of  external  work,  there  is,  as  was  observed 
by  Joule  and  Thomson,  a  certain  slight  cooling  effect  with 
most  gases.  With  a  perfect  gas  there  should  be  no  change 
in  temperature ;  the  observed  effects  are  therefore  due  to 


INTRODUCTION  n 

deviations   from   Boyle's   and   Joule's  I^aws,   Joule's  L,aw 
stating  that — 

U=>the  internal  energy  of  the  gas=>KT 

where  K  is  a  constant  and  T  the  absolute  temperature. 

The  cooling  effect  is  due  mainly  to  the  work  of  separation 
of  the  molecules  and  will,  therefore,  be  greater  as  the 
temperature  of  the  gas  is  lowered ;  similarly  the  effect  will 
be  greater  with  gases  which  are  not  much  above  or  are 
below  their  critical  temperatures.  Thus,  the  effect  is  much 
greater  for  carbon  dioxide  than  for  air,  while  with  hydrogen 
a  heating  effect  is  actually  observed  (cf.  p.  67).  On 
lowering  the  temperature  of  the  hydrogen,  however,  an 
inversion  point  is  reached  at  — 80:5°  C.  It  was  found  by 
Joule  and  Thomson  that  the  fall  in  temperature  could  be 
represented  by  the  expression — 


where   AT=the  fall  in  temperature  in  degrees  Centigrade 
and          A  =a  constant, 

while  according  to  the  more  exact  formula  of  Rose-Innes 
(Phil.  Mag.,  45,  (1898),  227)— 


where  A  and  B  are  constants.  The  latter  formula  indicates 
the  existence  of  an  inversion  point. 

The  Joule-Thomson  effect  forms  the  basis  of  the  L,inde 
process  for  the  liquefaction  of  air  and  is  dealt  with  more 
fully  on  p.  61. 

Specific  Heats  of  Gases.—  The  specific  heats  of  gases 
will  be  found  to  be  of  fundamental  importance  in  many 
questions  of  plant  design  as  well  as  in  thermodynamical 
calculations.  The  specific  heat  of  a  gas  varies  according 
as  to  whether  the  rise  or  fall  in  temperature  takes  place  at 
constant  pressure  or  at  constant  volume,  i.e.  with  or  without 
the  performance  of  external  work,  against  the  atmosphere. 
The  former,  Cp,  is,  of  course,  greater  than  the  latter,  C,,  the 


12  INDUSTRIAL   GASES 

difference  being  constant  and  equal  per  gram  molecule  of 
gas  to  R,  the  gas  constant,  R,  being  also  expressed  in  calories 
per  gram  molecule  of  gas. 
Thus— 

£p—  Cv=  R=  1-98  calories 

where  C^  and  Cv  are  the  molecular  heats. 

It  is  often  convenient  in  plant  design  to  express  thermal 
quantities  in  terms  of  pounds  and  degrees  Centigrade  and 
to  denote  the  resulting  units  as  C.H.U.  (Centigrade  heat 
units),  this  procedure  having  many  advantages  over  the 
B  .T.U.  system  using  Ibs.  and  degrees  Fahrenheit.  It  should  be 
noted  that  i  C.H.U./lb.=i  calorie/gram=i  kilocalorie/kilo. 

Further,  as  the  heat  capacities  of  most  diatomic  gases  for 
equal  volumes  are  equal  to  within,  say,  15  %,  it  is  often  con- 
venient to  express  the  same  in  terms  of  C.H.U./iooo  ft.3/0  C. 
Thus— 

The  specific  heat  at  constant  pressure  of  air  at  20°  C. 
=  0-2417  cals. /gram.  =  0-2417  C.H.U. /lb. 
=  0-2417  X 76-49  C.H.U./iooo  ft.s/°C.  at  15°  C. 
=  18-49  C.H.U./iooo  ft.3/°C. 

It  is  important  to  note  that  in  many  cases  the  specific 
heats  of  gases  vary  very  considerably  with  temperature  and 
pressure.  The  effect  of  increased  temperature  in  general 
is  to  produce  a  slow  increase  in  the  specific  heat ;  at  very 
low  temperatures,  however,  approximating  to  the  point  of 
liquefaction  of  the  particular  gas,  there  is  a  sudden  and 
very  marked  increase  in  the  specific  heat. 

The  effect  of  increased  pressure  is  also  to  produce  an 
increase  in  the  specific  heat,  thus,  the  specific  heat  at  constant 
pressure  of  air  increases  from  0-2415  at  i  atmosphere  to 
0*2925  at  200  atmospheres  (Holborn  and  Jakob,  Z.  Verein. 
deut.  Ing.,  58,  (1914),  1429),  an  increase  of  21  %.  The 
very  high  pressure  coefficients  found  by  I/ussana  (dm.,  [3], 
36,  (1894),  5,  70,  130)  are  undoubtedly  incorrect.  It  has 
been  found  that  the  ratio  CP/CV  is  a  constant  for  gases 
containing  the  same  number  of  atoms  in  the  molecule. 
The  approximate  value  for  monatomic  gases,  e.g.  argon, 


INTRODUCTION  13 

mercury  vapour,  etc.,  is  i'666,  for  diatomic  gases,  e.g. 
nitrogen,  1*41,  and  for  triatomic  gases,  e.g.  carbon  dioxide, 
i '30.  This  ratio,  usually  denoted  by  y,  is  of  importance  in 
connection  with  adiabatic  compression,  and  with  the 
propagation  of  sound  in  gases,  etc. 

Latent  Heats  of  Vaporization  and  Fusion.— When 
dealing  with  the  liquefaction  or  solidification  of  gases,  a 
knowledge  of  the  quantities  of  heat  required  to  effect  the 
change  in  question  is  necessary.  Particularly  is  the  thermal 
change  demanded  by  the  condensation  and  vaporization 
of  gases  important  in  connection  with  the  production  of 
cold  by  mechanical  means,  e.g.  through  the  intermediary 
of  ammonia  or  carbon  dioxide.  The  values  of  the  latent 
heats  of  vaporization  of  substances  decrease  with  rise  in 
temperature. 

Thermochemistry. — In  connection  with  plant  design,  an 
important  question  is  that  of  the  thermochemical  quantities 
concerned  in  the  different  reactions,  and,  in  the  case  of  new 
processes,  it  may  be  necessary  to  make  special  determina- 
tions of  the  same.  When  dealing  with  simple  combustion, 
this  can  be  easily  effected  by  means  of  the  Junker  calorimeter 
(cf.  p.  357)  or  other  like  instrument ;  if  the  gas  undergoing 
combustion  contains  hydrogen,  the  heat  of  combustion  may 
be  expressed  in  two  ways  :  (i)  gross,  i.e.  including  the  latent 
heat  of  vaporization  of  the  water  formed,  or  (2)  nett,  in  which 
case  this  quantity  is  deducted.  The  latent  heat  of  vaporiza- 
tion of  water  at  15°  C.  is  about  590  C.H.U./lb.,  or  10,600 
C.H.U./lb.  molecule. 

It  is  sometimes  the  custom  in  English  technical  practice 
to  consider  the  water  as  separated  at  100°  C.  with  the  heat 
evolution  of  538  C.H.U./lb.  water  and  to  deduct  this  quantity 
plus  the  heat  capacity  of  the  water  down  to  ordinary  atmo- 
spheric temperature  (6o°F.  =15-5°  C.),  equivalent  in  this  case 
to  84-5  C.H.U./lb.  water,  making  a  total  of  622-5  C.H.U./lb. 
water  (1120  B.T.U.). 

In  French  practice,  the  latent  heat  alone,  i.e.  538  C.H.U., 
is  deducted. 

Of  course,  neither  of  these  procedures  has  a  very  precise 
significance. 


14  INDUSTRIAL   GASES 

An  accurate  knowledge  of  the  heats  of  reaction  is  also 
of  fundamental  importance  in  connection  with  calculations 
of  gas  equilibria. 

Thermodynamical  Principles  Governing  Chemical 
Equilibria  in  the  Gaseous  State.  —  It  is  often  of  consider- 
able importance  to  be  able  to  make  an  approximate  forecast 
of  the  course  which  will  be  followed  by  a  reversible  gas 
reaction  of  which  the  equilibrium  data  have  not  been 
determined.  To  take  an  example,  consider  the  reaction 
represented  by  the  following  equation  — 

2CO^CO2  +  C  +  39,300  calories 

and  suppose  it  is  required  to  know  without  further  data, 
what  equilibrium  would  be  set  up  at  a  temperature  of  800°  C. 
under  atmospheric  pressure,  assuming  the  presence  of  an 
adequate  catalyst  and  sufficient  time  for  the  attainment  of 
equilibrium. 

The  theoretical  solution,  largely  due  to  Nernst,  requires 
more  space  than  can  be  allotted  in  the  present  volume.  It 
may  be  stated,  however,  that  Nernst  deduced  the  following 
formula  — 

.     (i) 


applying  to  an  equation  such  as  — 

mA  -f  m'E  ^  nC  +  n'D  +  H  calories. 

If,  for  the  sake  of  simplification,  we  adopt  the  convention 
that  the  heat  of  reaction,  Q,  is  taken  as  that  written  on  the 
same  side  of  the  equation  as  the  substances  occurring  in 
the  numerator  of  the  fraction  representing  K,  e.g.  in  the 
above  instance,  QT  =  H  when— 

_  ' 


PS 


pA  representing  the  partial  pressure  in  atmospheres  of  the 
constituent  A  in  the  final  equilibrium,  and  similarly  for 
B,  C,  andD. 

Then        Q0  =  heat  of  reaction  at  absolute  zero 

'  T-^j3T2  ....     (2) 


INTRODUCTION  15 

Sv  =  the  algebraic  sum  of  the  volumes,  those  on  the  right 
being  taken  as  positive  and  those  on  the  left  as 
negative, 
T  =  the  absolute  temperature, 


2T 

being  the  molecular  heat  of  each  constituent  at  tempera- 
ture T),  and 

3  the  algebraic  sum  of  the  chemical  constants  corre- 
sponding to  each  volume  of  gas  participating  in  the 
reaction,  those  on  the  right  being  taken  as  positive, 
those  on  the  left  as  negative,. 

For  most  purposes,  however,  it  is  permissible  to  neglect 
the  terms  correcting  for  the  effect  of  temperature  on  Q 
(equation  (2)),  and  to  omit  the  third  term  in  (i),  especially 
as  the  data  for  such  refinements  are,  in  many  cases,  lacking. 
We  then  have- 
log  K  =  — ^___  +  27vi  75  log  T  +  ZvC      .     (3) 

where  Q  =  heat  of  reaction  at  the  ordinary  temperature. 

If  one  or  more  constituents  be  solid  or  liquid  with  no 
appreciable  vapour  pressure,  e.g.  carbon  in  the  above  example, 
the  pressures  of  these  constituents  do  not  appear  in  the 
fraction  representing  K,  and  the  chemical  constants  are  not 
included  in  the  term  2vC. 

When  no  change  in  volume  occurs  during  the  reaction, 
the  term  ^175  log  T  disappears. 

The  Chemical  Constant. — The  undetermined  integration 
constant,  known  as  the  chemical  constant,  can  be  evaluated 
by  considerations  into  which  it  is  unnecessary  to  enter  here, 
and  values  as  follows  are  obtained  for  the  different  gases 
(cf.  also  I^angen,  Z.  Elektrochem. ,  25,  (1919),  25)  : 


16  INDUSTRIAL  GASES 


TABLE   4. 
CHEMICAL  CONSTANTS. 

Gas.  Chemical  Constants. 

Hydrogen       .............  r6 

Methane  ..............  2-5 

Nitrogen  ..............  2'6 

Oxygen     ..............  2'8 

Carbon  monoxide      ...........  3-5 

Chlorine   ..............  3-1 

Iodine       ..............  3-9 

Hydrochloric  acid     ...........  3-0 

Hydriodic  acid    ............  3-4 

Nitric  oxide   .............  3-5 

Nitrous  oxide       ............  3-3 

Sulphuretted  hydrogen        .........  3-0 

Sulphur  dioxide  ............  3-3 

Carbon  dioxide    ............  3-2 

Carbon  disulphide     ...........  3-1 

Ammonia  ..............  3*3 

Water  ...............  3-6 

Carbon  tetrachloride      ..........  3-1 

Chloroform    .............  3-2 

Benzene   ..............  3-0 

Ethyl  alcohol      ............  4-1 

Ether        ..............  3-3 

Acetone    ..............  3-7 

Propyl  alcohol     ............  3-8 

Returning  to  the  equation  in  question,  and  substituting 
the  appropriate  values  in  the  expression  — 


log  K  =  -         +  a*  75  log  T  + 
we  have  — 


log  q=i  =  —  zi3  --  j.^-   i        1,073  +  (3*2—  2  X  V 
'        X  1,073 


=  8-013—  5-304  —  3-8 

=  —1-091 

therefore  K  =  o-o8ii 

Boudouard's  experimental  value  for  this  temperature  was 
7%  carbon  dioxide,  i.e.— 


P2co      0-932 

representing  a  satisfactory  agreement,  the  closeness  of  which 
is  accidental.  In  most  cases,  the  agreement  is  considerably 
less  good  but  a  valuable,  if  approximate,  idea  of  the  equili- 
brium may  be  obtained  in  this  way. 


INTRODUCTION  17 

Velocity  of  Reaction. — The  velocity  of  chemical  re- 
action is  very  sensitive  to  changes  in  temperature,  and,  as  a 
rough  average  rule,  it  may  be  taken  that  the  velocity  doubles 
itself  with  each  10°  C.  rise  in  temperature. 

Further,  the  concentrations  of  the  react  ants  are  operative 
as  follows,  e.g.  in  the  homogeneous  bimolecular  reaction — 

A  +  B=^C    or    D  +  B 

if  a  and  b  are  the  initial  molar  concentrations  of  A  and  B, 
and  x  the  amount  of  either  which  has  undergone  combination 
at  time  t,  then — 

dx 

^=*kT(a-x)(b-x) 

where  &T  is  a  constant  for  temperature  T. 

Heterogeneous  Catalytic  Gas  Reactions. — Reaction 
Velocity — Output  and  Completeness. — By  heterogeneous  cata- 
lysis it  is  implied  that  there  is  a  discontinuity  between  the 
reactants  and  the  catalyst.  Nearly  all  the  important  cases 
of  technical  gas  catalysis  belong  to  this  category. 

In  most  heterogeneous  catalytic  gas  reactions,  e.g.  in 
the  direct  synthesis  of  ammonia,  we  are  dealing  with  the 
dual  effects  of  equilibrium  and  reaction  velocity.  Thus, 
on  working  with  a  fixed  pressure  and  a  moderate  gas  flow, 
and  gradually  raising  the  temperature  from,  say,  300°  C. 
to  900°  C.,  we  find  the  percentage  of  ammonia  in  the  effluent 
gases  increases  from  practically  zero  to  a  maximum  value 
in  the  region  of  500-600°  C.  (the  exact  temperature  depending 
on  the  catalyst  and  the  rate  of  flow),  and  then  falls  off  again. 
At  900°  C.,  even  with  an  indifferent  catalyst,  equilibrium — 
about  07%  NH3  at  100  atmospheres — is  almost  completely 
established,  whereas  at  a  low  temperature,  such  as  300°  C., 
although  the  equilibrium  value  is  some  52  %  at  100  atmo- 
spheres, the  reaction  velocity  is  so  low  that  practically  no 
ammonia  formation  takes  place.  This  example  is  typical 
of  the  phenomena  occurring  in  heterogeneous  catalytic 
reactions. 

Another  important  point  in  the  control  of  heterogeneous 
catalytic  gas  reactions  is  the  relation  between  the  velocity 
A.  2 


i8  INDUSTRIAL   GASES 

of  passage  of  the  reacting  gases  over  the  catalyst,  the  rate 
of  formation  of  the  product,  and  the  volume  occupied  by 
the  catalyst.  It  will  be  found  convenient  to  denote  the 
ratio  of  gas  velocity  per  hour  to  the  gross  catalyst  volume 
by  "  space- velocity,"  and  the  ratio  of  the  production  per 
hour  to  the  gross  catalyst  volume  by  "  space- time-yield." 
Using  these  terms  we  find  that  as  the  space- velocity  is 
increased  there  is  often  a  steady  increase  in  the  space- time- 
yield,  although  the  approach  to  equilibrium  in  the  reaction 
products  falls  off.  Thus,  taking  again  the  case  of  ammonia, 
as  the  space- velocity  is  increased  the  percentage  of  ammonia 
falls  off  but  the  production  per  unit  time  increases  (cf .  p.  215) . 
This  is  important  as  the  output  of  a  plant  is  thereby 
raised,  although  this,  of  course,  is  not  the  only  practical 
consideration. 

For  a  proper  understanding  of  these  phenomena  it  will 
be  necessary  to  examine  the  facts  a  little  more  closely,  and 
to  study  the  progress  of  such  reactions  with  time.  In  an 
investigation  of  the  catalytic  reaction— 

2SO2  +  O2  =  2SO3 

Bodenstein  and  Fink  (Z.  physik.  Chem.,  60,  (1907),  i,  45) 
found  that  the  rate  of  reaction  was  practically  independent 
of  the  concentration  of  oxygen,  was  proportional  to  the 
concentration  of  the  sulphur  dioxide  and  inversely  propor- 
tional to  the  square  root  of  the  concentration  of  the  sulphur 
trioxide — 

dx ,  (a  —  x) 

lit  ~         x* 

where  a  is  the  initial  concentration  of  the  sulphur  dioxide 
and  x  is  the  concentration  of  the  sulphur  trioxide,  i.e.  we 
have  a  modified  monomolecular  reaction,  whereas,  according 
to  the  laws  governing  homogeneous  reactions,  it  should  be 
ter  molecular. 

This  behaviour  was  explained  by  Bodenstein  on  the  so- 
called  "diffusion  theory,"  which  supposes  reaction  on  the 
surface  of  the  catalyst  to  be  extremely  rapid  but  that  access 
of  the  reactants  thereto  can  only  occur  by  diffusion  through 


INTRODUCTION  19 

an  adsorbed  film  of  the  reaction  product  —  in  this  case'  sulphur 
trioxide.  The  rate  of  reaction,  therefore,  is  dependent  on 
the  rate  of  diffusion  of  the  component  with  the  lower  coefficient 
of  diffusion,  namely,  sulphur  dioxide,  unless  a  sufficient 
excess  of  this  gas  be  present  when  the  rate  of  diffusion  of 
the  oxygen  begins  to  play  an  appreciable  part.  In  dealing 
with  such  reactions  it  is  difficult  to  formulate  any  general 
rules  as  to  the  reaction  kinetics  ;  thus,  in  the  reaction  — 

2CO  +  O2  =  2CO2 

Bodenstein  and  Ohlmer  (Z.  physik.  Chem.,  53,  (1905),  166) 
found  that  the  rate  of  reaction  was,  roughly,  inversely  pro- 
portional to  the  concentration  of  tne  carbon  monoxide,  a 
case  of  negative  catalysis. 

In  the  case  of  the  catalytic  combination  of  the  con- 
stituents of  electrolytic  gas,  Bone  and  Wheeler  (Phil.  Trans., 
A,  206,  (1906),  i)  found— 


where  COH^  and  C/H  are  the  concentrations  of  hydrogen  at 
the  beginning  and  at  time  t  respectively  ;  this  observation  is 
not  in  accordance  with  the  requirements  of  the  diffusion 
theory,  which  demands  that  the  rate  should  be  proportional 
to  some  function  of  the  oxygen  concentration,  this  being 
the  gas  of  slower  rate  of  diffusion. 

Taking  again  the  example  of  ammonia  synthesis,  a  mental 
picture  of  the  effect  of  velocity  of  passage  of  the  gases  over 
the  catalyst  may  be  formed  as  follows  :  imagine  the  speed 
of  passage  to  be  suddenly  increased  ;  if  we  assume  the 
rate  of  diffusion  of  the  reactants  through  the  ammonia 
film  to  remain  constant  momentarily,  the  rate  of  production 
will  be  unaltered  and  the  percentage  of  ammonia  in  the 
gases  will  fall  off.  The  thickness  of  the  film,  being  a  function 
of  the  concentration  of  the  ammonia,  will  now  diminish  as 
a  result  and  thus  permit  the  production  to  rise.  The 
degree  of  turbulence  of  the  gas  current  will  exert  a  certain 
influence  by  its  effect  in  reducing  "  pocketing  "  and  conse- 
quent local  formation  of  thick  ammonia  films. 


20  INDUSTRIAL   GASES 

Similar  considerations  apply  to  any  reaction  in  which 
a  solid  catalyst  is  used  to  promote  the  combination  of 
gaseous  substances  ;  in  some  cases  the  point  of  importance 
is  not  the  hourly  quantity  of  the  resulting  product  or  products, 
but  the  closeness  with  which  equilibrium  is  approached,  e.g. 
in  the  B.A.M.A.G.  continuous  catalytic  hydrogen  process 
(cf.  p.  159)  the  elimination  of  carbon  monoxide  is  the  most 
important  consideration,  being  balanced  by  the  desirability 
of  treating  a  given  volume  of  gas  in  the  least  possible 
catalyst  space. 

In  catalytic  operations  the  question  of  catalyst  surface 
is  of  great  importance,  the  output  of  a  given  gross  volume 
being  enhanced  by  the  increase  of  the  surface  of  the  catalyst, 
e.g.  by  subdivision  of  the  catalyst  mass,  although  the 
increased  resistance  set  up  thereby  makes  a  compromise 
necessary.  Calvert,  in  B.P.  10612/12,  suggests  increasing 
the  rate  of  catalysis  by  whirling  the  catalyst  inside  a  closed 
vessel  traversed  by  the  gas  current,  also  Walter,  in  D.R.P. 
295507/17,  proposes  to  agitate  the  catalyst  grains  by 
magnetic  means.  In  each  case  the  gain  in  output  is  secured 
without  the  usual  disadvantage  of  increased  dilution,  or, 
conversely,  a  close  approximation  to  equilibrium  is  facilitated 
without  the  necessity  for  such  slow  passage  of  the  gases. 
The  application  of  such  ideas,  however,  is  not  very  easy  in 
practice,  and  in  the  case  of  the  magnetic  agitation,  the  mutual 
attrition  of  the  catalyst  grains  would  be  prejudicial. 

In  the  patent  literature  relating  to  catalysis  considerable 
attention  has  been  paid  to  the  question  of  electrostatic 
activation  of  catalysts,  but  nothing  of  practical  importance 
would  appear  to  have  been  evolved  in  this  direction. 

Viscosity  of  Gases — Stream-Line  and  Turbulent 
Motion. — When  a  gas  (or  other  fluid)  flows  through  a 
conduit  under  certain  conditions — see  below — the  gas  moves 
at  a  higher  velocity  in  the  centre  than  in  the  layers  nearer 
the  walls,  while  the  layer  contiguous  to  the  walls  is 
stationary. 

Viscosity  is  defined  as  the  tangential  force  exerted  per 
unit  area  between  two  layers  in  the  fluid  i  cm.  apart, 


INTRODUCTION  21 

when  the  difference  in  velocity  is  i  cm.  /sec.  for  flow 
through  a  tube,  the  viscosity  (p,)  is  given  approximately 
by  the  expression  — 


where  p  =  the  pressure  drop  in  dynes/cm.2, 
r  =  radius  of  tube  in  cms., 
t  —  time  in  seconds  required  for  the  passage  of  V  c.c. 

of  fluid  (measured  at  the  mean  pressure), 
/  =  length  of  the  tube  in  cms. 

The  viscosity  of  gases  increases  considerably  with  rise 
in  temperature,  cf.  Table  12  (c). 

An  interesting  fact  is  that  the  viscosity  of  gases  is  approxi- 
mately independent  of  the  pressure,  i.e.  the  volume  of  gas 
at,  say,  200  atmospheres  pressure,  flowing  through  a  given 
tube  with  a  certain  pressure  drop  will  be  approximately  the 
same  per  unit  of  time  as  that  observed  for  an  equal  pressure 
drop  with  gas  at  atmospheric  pressure  ;  the  weight  of  gas, 
however,  will  be  some  200  times  as  great. 

The  above  observations  hold  only  for  stream-line  motion 
through  conduits,  i.e.  in  the  complete  absence  of  turbulence. 
When  a  fluid  passes  through  a  straight  smooth  circular 
tube,  the  motion  remains  of  the  stream-line  type  until  a 
certain  definite  velocity  —  known  as  the  critical  velocity  —  is 
reached,  when  turbulence  sets  in  abruptly  and  increases 
steadily  in  degree  as  the  velocity  is  further  increased.  The 
pressure  drop  increases  sharply  with  the  inception  of  turbu- 
lence and  is  no  longer  defined  by  the  expression  just  given, 
being  now  determined  by  the  surface  friction. 

The  critical  velocity  is  given  by  the  following  expression  — 

25001* 

vc=   J7  r  cm.  /sec. 
dp 

where  ju,  =  the  viscosity  of  the  fluid  in  C.G.S.  units, 
d  =3  diameter  of  the  tube  in  cms., 
p  =  the  density  of  the  fluid  in  grams/cm.3, 
vc  =  the    critical  velocity   (mean    linear    velocity)   in 
cm.  /sec., 


22  INDUSTRIAL  GASES 

i.e.  vc  is  directly  proportional  to  the  viscosity  of  the  fluid 
and  inversely  proportional  to  the  diameter  of  the  tube  and 
to  the  density  of  the  fluid.  This  applies  generally  to  all 
fluids  (cf.  Stan  ton  and  Pannell,  Phil.  Trans.,  A.,  214,  (1914), 
199). 

In  some  cases  it  may  be  more  convenient  to  express 
partly  in  terms  of  British  units,  thus — 

2000/A  ,.    . 

vc  = -f-  ft. /sec. 

pa 

or  Qc  =  40,000  ^—  ft.3/hr. 

P 

where  vc  =  critical  velocity  (mean  linear  velocity)  in  ft./sec., 
ft  =>  viscosity  in  C.G.vS.  units, 
p  —density  of  the  fluid  in  lbs./ft.3, 
d  =  diameter  of  the  tube  in  inches, 
Qc  =  the   minimum  gas  flow,  measured  at   the   tem- 
perature and  pressure  used,  at  which  turbulent 
motion  obtains,  in  ft.3/hr. 

It  must  not  be  imagined  that  the  flow  in  a  given  conduit 
is  necessarily  stream-line  motion  because  the  velocity  is 
below  that  given  in  the  above  formula  ;  unstable  turbulence 
may  be  set  up  by  local  irregularities,  bends,  etc.  The 
turbulence  will  die  away,  however,  if  sufficient  time  be 
allowed  and  the  re-establishment  of  stream-line  motion  may 
be  accelerated  by  the  insertion  in  the  stream  of  a  series  of 
perforated  grids. 

Resistance  to  Flow  of  Gases. — In  technical  gas 
manufacture  and  usage,  the  calculation  of  the  pressure 
drop  in  a  given  pipe-line  is  an  important  point,  the  resistance 
to  flow  often  constituting  the  source  of  a  considerable  power 
expenditure.  The  following  formula  gives  fairly  good 
results  for  turbulent  motion  in  smooth,  straight,  circular 
pipes  (cf.  Newbiggin's  "Handbook  for  Gas  Engineers  and 
Manufacturers  "  :  Condon,  1913,  p.  276)  : — 

dp  =--&%-  -Ibs./in.* 
^        II  X  I06  X  rf5          ' 


INTRODUCTION 


where  Q  =  ft.3/hr.  of  gas,  measured  at  the  temperature  and 
pressure  in  question,  passing  through  the  tube, 
p  =  density  of  the  gas  in  lbs./ft.3 
Iv  =  length  of  the  tube  in  feet, 
d  =  diameter  in  inches. 

The  formula  assumes  that  the  pressure  drop  is  propor- 
tional to  the  square  of  the  linear  velocity,  which  assumption 
is  not  strictly  correct  especially  as  no  account  is  taken  of  the 
state  of  turbulence  or  otherwise  of  the  fluid.  Thus,  with 
stream-line  motion  the  pressure  drop  is  proportional  to  the 
first  power  of  the  linear  velocity.  A  more  exact  treatment 
is  furnished  by  an  experimental  investigation  by  Stanton 
and  Pannell  (loc.  cit.)  giving  rise  to  a  general  curve  which 
connects — 

R         .,  «       2Vrp      i       2Qp 

-vj-v  I         _      -    1  s^r*  ***** 


(Fig.  3) 


0-007 
0-006 
0-005 
0-004 

& 

0-003 
0002 
0-001 

\ 

\    r 

^ 

\! 

\^ 

_1^_  

^^ 

-•—  

3-Q 


5-5 


4-0 


4-5 


5-0 


5-5 


FIG.  3.  —  Stanton  and  Pannell's  Surface  Friction  Determinations. 

and  covers  the  whole  range,  including  the  transition  from 
stream-line  to  turbulent  motion,  and,  moreover,  is  applicable 
to  all  fluids,  whether  liquid  or  gaseous. 

R  =>  resistance  per  unit  area  of  the  internal  surface   of 

the  circular  tube, 
p  =  density  of  the  fluid, 


24  INDUSTRIAL   GASES 

V  =»  mean  linear  velocity, 

r  =j  radius  of  tube, 

/z  =»  viscosity  of  the  fluid, 
all  in  absolute  units. 

The  pressure  drop  in  a  given  circular  tube  is  given  by 
the  expression  — 


,  .       2/oQ2/C  -  2pQ2/C 

dp  =     r~6     dynes/cm.2  =  approximately      g  2  6  atms. 

where  p  =  density  of  the  fluid  in  grams/cm.3 
Q  =3  flow  through  the  tube  in  cm.3/sec. 
V  =i  mean  linear  velocity  of  the  fluid  in  cm./sec. 
/   =»  length  of  tube  in  cms. 
r  =  radius  of  tube  in  cms. 
C  —  R/pV2  as  read  off  from  the  curve  (Fig.  3). 
p    —  viscosity  of  the  fluid  in  C.G.S.  units. 

The  above  observations  apply  only  to  smooth  and  straight 
circular  conduits.  The  effect  of  abrupt  bends,  valves,  local 
constrictions,  and  also  of  enlargements  in  the  section  of  the 
pipe  is  to  introduce  large  effects  which  may  be  equivalent  to 
many  feet  of  the  plain  conduit,  and  often  constitute  the 
most  important  cause  of  pressure  drop  in  technical  opera- 
tions. The  theoretical  treatment  of  such  effects  is  a  difficult 
matter,  although  certain  rough  empirical  generations  can 
be  deduced  from  experience. 

A  good  opportunity  of  testing  the  validity  of  a  general 
formula,  such  as  that  of  Stanton  and  Pannell,  is  afforded  by 
application  to  the  little  investigated  question  of  the  loss  of 
head  in  the  flow  of  high-pressure  gases  through  tubes  ;  in 
the  experience  of  the  author,  this  formula  gives  valuable 
indications  of  the  resistance  under  these  conditions. 

Influence  of  Difference  in  Level.  —  When  making 
allowances  for  the  drop  in  pressure  due  to  dynamic  effects, 
due  consideration  should  be  given  to  the  static  head  if  any 
considerable  difference  in  level  occurs,  especially  with  very 
light  or  heavy  gases. 

Consider  a  pipe,  open  at  one  end  and  filled  with  a  gas  of 


INTRODUCTION  25 

density  pi,  while  that  of  the  surrounding  medium*  e.g.  air, 

Then,  in  absolute  units,  the  pressure  difference  due  to 
the  difference  in  weight  of  the  gases — 

=  ±  hg  (Pi  —  P2>  dynes, 

where  h  =  the  vertical  difference  in  height  in  cms., 
and  g  =3  the  gravitational  constant  in  C.G.S.  units, 
=  ±  h  (p1  —  p2)  grams. 

Expressing  h  in  ft.,  and  px,  p2  in  lbs./ft.3,  and  taking 
the  case  of  a  difference  in  level  equal  to  100  ft.,  with  hydrogen 
in  the  pipe,  at  15°  C.,  we  have — 

pressure  difference  =-^(5:32-76'49)  lbs /ft  2 

1000 

=  7-117  lbs./ft.2 
=  0-494  lbs./in.2 
=  13*7  inches  of  water. 

Physical  Methods  of  Testing  the  Purity  of  Gases.  - 

In  special  cases  it  is  advisable  to  be  able  to  determine  the 
quantity  of  some  specific  impurity  present  in  a  particular 
gas,  by  physical  means,  either  from  reasons  of  speed  or  for 
purposes  of  automatic  recording.  Among  such  methods 
may  be  mentioned  the  following : — 

Gas  Interferometer. — This  instrument  was  worked  out  by 
Haber  and  Iy6we  (Z.  angew.  Chem.,  (1910),  1393).  Its  action 
depends  on  the  formation  of  interference  fringes  by  two 
columns  of  gases,  one  containing  the  impurity  to  be  deter- 
mined, e.g.  carbon  dioxide  in  air,  and  the  other  free  from  this 
impurity.  The  apparatus  can  be  made  extremely  sensitive 
but  is  somewhat  cumbersome  and  does  not  lend  itself  readily 
to  the  production  of  mechanical  records.  For  technical 
adaptations,  cf.  "U.S.  Bureau  of  Mines,"  Tech.  Paper, 
No.  185  (1918),  by  Siebert  and  Harpster. 

Density. — The  density  of  a  gas  is  often  a  good  guide  to 
its  purity,  particularly  in  the  case  of  hydrogen,  and  a 
convenient  apparatus  for  indicating  the  same  is  the  "  gas 
balance,"  which  consists  of  a  balance  beam,  one  arm  of  which 


26  INDUSTRIAL  GASES 

carries  a  ball  supplied  with  a  continuous  current  of  gas 
by  means  of  mercury  cups  near  the  fulcrum  of  the  beam, 
while  the  other  carries  a  pointer.  The  balance  is  brought 
into  equilibrium  by  means  of  riders. 

Effusion. — The  purity  of  a  gas,  e.g.  the  percentage  purity 
of  hydrogen  containing  small  quantities  of  nitrogen,  oxygen, 
carbon  monoxide,  etc.,  may  also  be  ascertained  by  the  rate 
of  effusion  through  a  fixed  small  aperture.  For  this  purpose 
an  inverted  glass  cylinder,  immersed  in  a  cylinder  containing 
water,  or  a  small  water-sealed  metal  gasholder  provided  with 
a  balance  weight  (this  form  being  made  by  Messrs.  Wright 
&  Co.),  is  filled  to  a  fixed  mark  with  the  gas  in  question, 
and  the  time  required  for  the  gas  to  flow  out  through  a  fine 
orifice  in  a  piece  of  platinum  foil,  i.e.  the  time  for  the  cylinder 
or  bell  to  fall  to  another  fixed  mark,  is  noted.  A  comparison 
with  a  standard  gas,  e.g.  air,  or  preferably  a  sample  of  the 
pure  gas,  say  hydrogen,  if  this  be  the  gas  under  examination, 
gives  the  density  on  the  basis — 

p  oc  t2 

where  p  =  the  density  of  the  gas, 
t  =  the  time  of  outflow. 

Determinations  with  this  apparatus  occupy  only  a  few 
minutes ;  the  results,  of  course,  are  not  of  a  high  degree  of 
accuracy. 

Acoustical  Methods. — A  method  was  worked  out  by  Haber 
and  L,eiser  (J.  Soc.  Chem.  Ind.,  (1914),  54)  for  the  detection 
of  methane  in  mine  gases,  depending  on  the  difference  in 
sound  produced  by  two  whistle  tubes  filled  with  pure  air 
and  mine  air  respectively,  but  separated  by  means  of  thin 
mica  plates  from  the  actual  whistles,  both  of  which  are 
operated  by  the  mine  air. 

Separation  of  Gaseous  Mixtures.— Special  cases  of 
separation  will  be  dealt  with  in  particular  instances,  e.g. 
the  separation  of  air  into  its  various  constituents,  but  a 
short  jforecast  here  of  the  possible  methods  will  be  useful. 
It  is  interesting  to  note  that  a  certain  irreducible  amount 
of  work  must  be  expended  on  a  gaseous  mixture  to  separate 


INTRODUCTION  27 

it  into  its  components,  equal  to  the  work  of  fsothermal 
compression  of  each  constituent  from  its  original  partial 
pressure  to  atmospheric  pressure  or  whatever  the  final 
pressure  may  be;  cf.  p.  80. 

Among  the  various  methods  of  separation,  the  following 
are  the  most  important : — 

(1)  Chemical  methods': 

(2)  By  liquefaction  of  one  of  the  constituents. 

(3)  By  fractional  solution  in  water  or  other  medium. 

(4)  By  fractional  diffusion  through  platinum  or  porous 

earthenware,  etc. 

(5)  By  centrifugal  action. 

It  may  be  noted  that  (i)  and  (2),  and  in  some  cases  (3), 
are  the  only  methods  which  have  any  technical  importance. 

Separation  of  Liquid  or  Solid  Particles  from  Gases. 
— In  the  technical  manipulation  of  gases  it  is  frequently 
necessary  to  free  a  gas  from  some  suspended  liquid  or  solid 
impurity,  e.g.  in  the  manufacture  of  coal  gas,  the  separation 
of  the  "  tar  fog  "  is  a  matter  of  considerable  difficulty, 
while  in  the  concentration  of  sulphuric  acid  in  Gaillard 
towers,  the  exit  gases  are  liable  to  contain  sulphuric  acid  in 
suspension.  Without  entering  into  details  it  will  be  useful 
to  indicate  the  methods  used  in  practice  for  the  elimination 
of  liquid  or  solid  particles  from  gases. 

This  object  may  be  achieved  by  direct  filtration  through 
sawdust,  or  by  wetted  gauze.  A  method  frequently  adopted 
for  the  separation  of  suspended  matter  present  in  considerable 
quantity,  e.g.  in  the  manufacture  of  white  arsenic,  is  to  subject 
the  gases  to  centrifugal  force  by  causing  them  to  traverse  a 
circular  path  or  by  means  of  a  special  fan ;  this  throws  out 
the  bulk  of  the  dust,  the  centrifugal  separation  being  usually 
followed  by  bag  filtration.  The  centrifugal  separation  in 
the  fan  is  sometimes  assisted  by  the  injection  of  water. 

Other  methods  depend  on  the  use  of  gas  velocities 
sufficiently  low  to  allow  precipitation  of  heavy  dusts  to 
occur,  while  considerable  success  has  attended  the  use  of 
abrupt  changes  in  direction  by  means  of  baffles,  the  action 
being  parallel  to  that  occurring  with  centrifugalization. 


28  INDUSTRIAL  GASES 

In  the  case  of  "  tar  fog  "  and  the  like,  passage  through  a 
number  of  small  orifices  or  slits,  followed  by  scrubbing  with 
liquids,  is  often  adopted. 

Another  mode  of  attack  is  to  precipitate  the  dust  by 
the  formation  of  a  mist  on  producing  a  condition  of  super- 
saturation  in  the  gas,  e.g.  in  the  removal  of  dust  from  the 
gases  leaving  mechanical  pyrites  burners  by  addition  of 
steam  and  sulphur  trioxide,  the  resulting  mist  being  subse- 
quently removed  by  electrostatic  precipitation  or  by  other 
means  (Holler,  D.R.P.  270757/12).* 

The  most  searching  method,  however,  is  that  depending 
on  electrostatic  action,  rendered  practical  by  Cottrell,  and 
at  the  present  time  attracting  considerable  attention.  On 
passing  a  dust-laden  gas  in  proximity  to  two  highly  charged 
electrodes,  the  gas  is  ionized  and  the  particles  becoming 
charged  move  in  the  direction  of  the  electrode  of  opposite 
charge.  If  one  electrode  is  pointed  the  particles  tend  to 
become  charged  with  the  polarity  of  this  electrode  and, 
consequently,  to  move  to  the  other  electrode. 

The  usual  method  of  operating  is  to  pass  the  gases  with 
linear  velocity  not  exceeding  about  12  ft./sec.  through  metal 
tubes  of,  say,  about  i  ft.  in  diameter,  enclosing  axially 
disposed  wires,  a  unidirectional  potential  difference  of  from 
25,000  to  250,000  volts  being  applied.  The  dust  is  deposited 
on  the  tubes  and  periodically  dislodged  by  interrupting  the 
gas  current  and  the  electrical  supply  and  by  jarring  the  tubes. 

The  process  is  largely  used  in  the  removal  of  dust  from 
the  gases  leaving  pyrites  burners ;  for  the  precipitation  of 
cement  dust,  which  contains  valuable  quantities  of  potash  ; 
for  the  precipitation  of  white  arsenic,  avoiding  the  handling 
necessary  in  "  bag-houses  "  ;  in  treating  the  effluents  of 
Gaillard  towers,  etc.  Some  trouble  is  experienced  in  the 
presence  of  solids  and  liquids  in  conjunction.  The  uni- 
directional current  is  best  obtained  by  means  of  a  rotating 
commutator,  operated  in  synchronism  with  a  high  tension 

*  An  ingenious  proposal  is  made  by  Mond  in  B.P.  112153/16,  to  effect 
the  removal  of  constituents  from  gaseous  mixtures  by  first  injecting  a 
suspension  of  some  solid  which  combines  with  or  absorbs  the  constituent 
in  question  and  subsequently  separating  the  dust  by  suitable  means. 


INTRODUCTION 


29 


transformer;  the  power  consumption  is  of  the 'order  of 
from  1-8  K.W.H.  per  million  ft.3  of  gas  treated  (cf.  Bush, 
/.  Soc.  Chem.  Ind.,  (1918),  38911).  The  process  is  applicable 
to  gases  at  fairly  high  temperatures  ;  it  is  important  to 
avoid  conditions  leading  to  the  condensation  of  moisture. 

Methods  of  Measuring  Volumes  and  Rates  of  Flow 
of  Gases.- — One  of  the  most  convenient  methods  of  measuring 
the  volumes  or  rates  of  flow  of  gases  through  a  given  conduit, 
when  the  quantities  are  not  too  large,  is  that  depending  on 
the  use  of  the  familiar  rotary  (wet)  meter  or  the  reciprocat- 
ing (dry)  meter.  The  former  consists  of  a  series  of  inverted 
buckets,  mounted  on  a  wheel  with  a  horizontal  spindle,  and 
immersed  in  a  tank  of  water,  the  wheel  revolving  at  a  rate 
proportional  to  the  volume  of  gas  entering  the  buckets. 
Such  meters  are  constructed  in  sizes  up  to  about  150,000 
ft.3/hr.  They  are  very  sensitive  to  the  level  of  the  water 
and  calibration  at  frequent  intervals  is  important  when 
using  for  accurate  laboratory  work.  If  accuracy  be  required, 
it  is  necessary  to  allow  for  the  volume  of  water  vapour 
present,  the  effect  of  saturating  the  gas  with  water  vapour 
at  15°  C.  being  to  increase  the  volume  by  17  %.  Rotary 
meters  of  the  anemometer  type  are  convenient  when  dealing 
with  large  gas  flows,  especially  as  very  little  pressure  drop  is 
introduced.  Meters  capable  of  measuring  the  volume  of 
the  gas  at  pressures  greater  than  atmospheric,  e.g.  "high- 
pressure  "  coal  gas,  natural  gas,  etc.,  are  also  constructed. 

In  many  technical  operations,  however,  one  has  to  deal 
with  very  large  currents  of  gases,  e.g.  in  chimneys,  or  it  may 
be  desirable  to  measure  or  to  record  continuously  the  rate 
of  flow  in  a  given  conduit  of  large  diameter ;  in  such  cases 
it  is  necessary  to  make  use  of  some  kind  of  flow-meter. 
The  measurement  for  relatively  small  conduits  may  be 
effected  by  the  use  of  an  "  orifice  meter,"  which  consists  of 
a  perforated  diaphragm  introduced  into  the  conduit  and 
depends  on  observation,  usually  by  means  of  a  U-tube 
containing  a  suitable  liquid,  of  the  pressure  drop  caused  by 
the  constriction.  The  pressure  drop  varies  roughly  as  the 
square  of  the  gas  flow  and  is  rather  sensitive  to  temperature 


30  INDUSTRIAL   GASES 

variations.  The  Ventuii  meter  employs,  instead  of  a 
simple  orifice,  a  stream-line  constriction.  The  increase  in 
velocity  gives  rise  to  a  fall  in  pressure  in  the  constriction, 
but  to  only  a  very  slight  difference  across  the  same  ;  the  fall 
in  pressure  varies  roughly  as  the  square  of  the  gas  flow. 

When  the  size  of  the  conduit  becomes  great,  say  more 
than  i  ft.  in  diameter,  the  use  of  an  orifice  meter  is  in- 
convenient, especially  as  it  introduces  into  the  system  a 
pressure  drop  which  may  involve  the  expenditure  of  con- 
siderable amounts  of  energy.  In  such  cases  it  is  possible 
to  employ  an  anemometer,  i.e.  a  series  of  vanes  with  a 
train  of  recording  dials,  or  to  measure  the  "  drag  "  on  a 
bucket  or  plate  suspended  in  the  path  of  the  stream,  or, 
more  commonly,  use  is  made  of  a  Pitot  tube,  of  which  the 
indications  are  more  easily  converted  into  velocity  figures  ; 
if  made  of  glass,  it  is  unaffected  by  corrosive  gases  or  vapours. 

This  apparatus  consists  of  tubes  arranged  as  in  Fig.  4 
(cf.  Pannell,  Engineering,  (1919),  261).  The  side  openings 
(3  rows  of  7  holes  0-04"  diameter)  are  under  the  static 
pressure  existing  in  the  conduit,  while  the  central  tube  has, 
in  addition,  the  dynamic  head  due  to  the  local  arrestment 
of  the  current ;  consequently,  by  connecting  the  ends  A  and  B 
to  a  suitable  manometer,  a  pressure  difference  is  registered 
which  is  connected  with  the  linear  velocity  of  the  current 

as  follows  : —  / — - 

v  =  v  2gh 

where  v  =•  the  linear  velocity  at  the  point  of  the  Pitot  tube, 

in  cm. /sec., 

g  =  0,81  cm./sec.2  (the  gravitational  constant), 
h  =>  the  height  of  the  gas  column  equivalent  to  the 

head  of  liquid  in  the  manometer. 

If  the  indicating  liquid  be  water  and  the  moving  gas  be 
air,  both  at  15°  C.,  the  expression  becomes — 


x 


G'001226 

=»  I264'5'\/A'  cm./sec. 
where  h'  is  the  head  of  water  in  cm. 


INTRODUCTION 


Converting  into  the  more  practical  units  of  ft./sec.  and 
inches  of  water,  we  have — 

t._  1264-5 V*"X  2-54  f 

12  X  2'54 

=  66-1 VF' ft./sec. 

where  u  =>  the  linear  velocity  in  ft.-sec. 
h"  =>  the  head  of  wafer  in  inches. 


•I* 


-0-307 


FIG.  4.— Pitfit  Tube. 

Thus,  a  linear  velocity  of  20  ft./sec.  of  air  at  15°  C.  would 
give  a  head  of  water  equal  to — 


20 


. 

m.  -0-092  in. 


It  is  easy  to  see  how  corrections  for  density,  temperature 
and  pressure  of  the  gas,  or  for  density  of  the  indicating 
liquid  must  be  applied.  In  any  case  the  readings  do  not 
give  the  mean  linear  velocity  in  the  conduit  as  the  velocity 


32  INDUSTRIAL  GASES 

varies  from  point  to  point,  being  greatest  at  the  centre  and 
zero  at  the  walls.  With  stream-line  motion  the  mean 
linear  velocity  is  about  0-5  that  of  the  axial  velocity  ;  at 
the  critical  velocity  the  ratio  increases  sharply  to  a  value  in 
the  neighbourhood  of  0'8  (cf.  Stanton  and  Pannell,  loc.  cit.). 

The  Pitot  tube  has  many  disadvantages  :  it  involves 
the  use  of  a  delicate  manometer,  i.e.  a  tilting  gauge  in  which 
a  differential  brine  (S.G.,  i'o6)  and  castor-oil  combination 
is  often  used  instead  of  water  for  the  measurement  of  the 
very  small  pressure  difference  (cf.  Stanton,  Proc.  Inst.  Civil 
Eng.,  Civ VI.,  (1904),  78),  the  readings  being  unsuitable  for 
observation  by  a  workman. 

Recently,  considerable  attention  has  been  directed, 
therefore,  to  the  question  of  "  hot-wire  anemometry."  A 
general  description  by  Thomas  of  the  relative  advantages 
of  this  system  of  measurement  will  be  found  in  /.  Soc. 
Chem.  Ind.,  (1918),  i65T.  A  thin  wire,  preferably  of  plati- 
num, about  0*003  in.  in  diameter,  is  mounted  either  in  the 
centre  or  at  some  other  point  in  the  conduit  at  which  the 
relation  of  the  actual  to  the  average  linear  velocity  is  known. 
The  wire,  heated  electrically,  preferably  to  about  200°  C., 
forms  one  arm  of  a  Wheatstone  bridge  and  the  temperature 
fall  produced  by  the  gas  current  may  be  determined  by 
measurement  of  the  resistance  which,  of  course,  decreases 
with  fall  in  temperature. 

Calibration  may  be  effected  by  checking  against  measure- 
ments obtained  by  other  means  or  by  calculation  (cf .  Morris, 
Engineering,  (1912),  892).  The  expression  for  the  heating 
energy  (co)  for  a  particular  temperature  is  Ceo  =  \/v  -+-  k, 
where  v  —  linear  velocity  and  C  and  k  are  constants.  Small 
changes  in  the  pressure  or  temperature  of  the  gas  have  no 
appreciable  influence  on  the  results  if  these  be  expressed 
in  terms  of  mass  of  gas,  not  of  actual  linear  velocity.  The 
measurements  are  easily  taken  by  a  workman  and  can  be 
recorded  automatically,  if  desired. 

Since  the  indications  of  the  apparatus  are  considerably 
affected  by  turbulence  of  the  gas  under  examination,  it  is 
desirable  that  the  hot  wire  should  be  removed  from  proximity 


INTRODUCTION  33 

to  any  bends  or  valves  which  often  introduce  o'r  modify 
existing  turbulence  in  a  marked  degree. 

When  gases  which  are  decomposed  by  even  gentle 
heating  in  contact  with  a  heated  metal  surface,  e.g.  coal 
gas,  are  to  be  dealt  with,  the  platinum  wire  may  be  coated 
with  glass  which,  although  it  introduces  a  lag,  does  not 
affect  the  validity  of  the  relation  between  the  resistance 
of  the  wire  and  the  gas  velocity.  By  using  two  wires 
disposed  transversely  in  the  stream,  one  close  behind  the 
other,  the  direction  of  motion  can  be  followed,  as  the  down- 
stream wire  is  partly  shielded  from  cooling  by  being  swept 
by  the  heated  gas  leaving  the  other. 

Automatic  Safety  and  Purity  Tests. — In  the  routine 
control  of  technical  gas  reactions  or  treatments  it  is  often 
desirable  to  make  automatic  tests — preferably  capable  of 
giving  continuous  records — of  the  percentage  of  specific 
impurities  at  different  points  of  the  plant.  A  familiar 
example  of  a  recording  gas  analysis  apparatus  is  the  carbon 
dioxide  recorder,  which  is  chiefly  used  as  a  check  on  the 
combustion  in  boilers  and  the  like.  The  most  usual  form, 
e.g.  the  Sarco  apparatus,  depends  on  the  automatic  measure- 
ment by  the  position  of  a  small  balanced  gasholder,  of  a 
sample  of  gas  before  and  after  exposure  to  caustic  soda 
solution.  A  filter  pump  or  a  stream  of  water  is  used  to 
provide  the  necessary  power  for  sucking  in  and  ejecting 
the  gases  ;  the  result  of  each  analysis  is  registered  by  a  pen 
attached  to  the  little  gasholder  on  a  drum  rotated  by  clock- 
work, the  intervals  between  successive  analyses  being  about 
five  minutes. 

In  another  form,  a  bi-meter  recorder,  made  by  the 
Cambridge  Scientific  Instrument  Co.,  a  continuous  stream 
of  gas  is  passed  through  two  gas  meters,  between  which  is 
interposed  a  lime  or  soda-lime  absorber.  The  difference  in 
the  readings  gives  the  percentage  of  carbon  dioxide.  On 
similar  lines  is  the  form  of  apparatus  in  which  two  orifice 
gauges  are  used  with  soda-lime  interposed  (/.  Gasbeleucht., 
1914,  548).  Other  methods  operate  through  the  measure- 
ment of  the  heat  of  absorption  of  carbon  dioxide  by  alkalis. 
A.  3 


34  INDUSTRIAL    GASES 

For  the  automatic  detection  or  determination  of  either 
oxygen  or  combustible  gases  in  admixture  with  each  other, 
e.g.  the  oxygen  content  of  electrolytic  hydrogen  or  the 
presence  of  methane  in  mine  air,  methods  have  been  pro- 
posed, depending  on  the  measurement  of  the  rise  in  tempera- 
ture produced  by  catalytic  combination  in  the  presence 
of  platinum  black  or  the  like  at  the  ordinary  temperature, 
by  means  of  air  thermometers  or  by  the  change  in  resistance 
of  wires  coated  with  a  catalyst  (cf.  lounge's  "  Gas  Analysis," 
1914).  Hither  method  can  be  adapted  to  giving  an  alarm 
automatically  or  to  furnishing  a  continuous  record.  These 
methods  have  some  disadvantages,  to  overcome  which 
an  apparatus  has  been  devised  by  Greenwood  and  Zealley 
(/.  Soc.  Chem.  Ind.,  (1919),  87 T),  depending  on  the  automatic 
measurement  of  the  contraction  resulting  from  the  inter- 
mittent heating  of  a  platinum  wire  in  the  gas  mixture. 

Only  a  few  examples  have  been  given  above,  but  they 
are  typical  and  will  serve  to  indicate  the  general  mode  of 
attack  in  special  cases. 

The  Compression  of  Gases. — This  is  a  very  important 
consideration,  since  most  of  the  gases  prepared  technically 
are  put  on  the  market  compressed  to  120  atmospheres. 

Work  of  compression. — It  will  be  well  to  consider  the 
principles  determining  the  expenditure  of  energy  required 
to  effect  the  compression  of  gases  as  this  energy  con- 
stitutes an  important  item  in  the  cost  of  the  market- 
able gas. 

In  the  first  place  it  may  be  stated  that  in  technical 
practice  the  compression  approximates  rather  to  adiabatic 
than  to  isothermal  compression  although  efforts  are 
made  to  minimize  the  increase  in  power  involved  thereby 
by  adding  water,  the  vaporization  of  which  reduces  the 
temperature  rise,  and  by  effecting  the  compression  in  a 
number  of  stages,  which,  as  explained  later,  operates  in  the 
same  direction. 

Adiabatic  compression. — Consider  a  volume  of  gas  v\  at 
a  pressure^  when  the  temperature  (absolute)  is  Tj. 

Assume  this  gas  to  be  compressed  in  an  adiathermic 


INTRODUCTION  35 

• 
cylinder  to  a  pressure  of  p%,  the  volume  falling  to  v%  and 

the  temperature  rising  to  T£. 

Now  in  this  process  the  product  pvy  will  remain  constant, 
where 


equals  the  ratio  of  the  specific  heats  at  constant  pressure 
and  constant  volume  respectively,  or 


where  C  is  a  constant. 

The  work  of  this  adiabatic  compression  (Wj)  equal 

C 

.dv  =  ——(v1l-v  —  v2*~v) 
i—  yv 

Substituting  C  ^piV^  =*ptf)$  we  have  — 


vi 
p. 


wl 


•Rut 


We  have  now  compressed  the  gas  to  the  required  pressure, 
but  its  temperature  is  — 


in  accordance  with  the  law  for  the  effect  of  adiabatic  com- 
pression from  pi  to  p%. 

In  order  to  reduce  its  temperature  to  Tx,  the  initial 
temperature,  we  will  consider  the  walls  of  the  cylinder  to 
become  conducting.  To  prevent  the  pressure  falling,  it 
will  be  necessary  to  follow  up  the  contracting  gas  with  the 


36  INDUSTRIAL    GASES 

piston,  a  further  amount  of  work  (W2)  being  thus  performed 
on  the  gas. 

The  volume  after  cooling  to  TI  will  be  —  - 

Pi 

*\ 

assuming  Boyle's  I,aw  to  be  valid. 

Therefore,  the  volume  before  cooling,  i.e.  at  T2,  will  be  — 

Pi   ?2 
•*/jk  -*F 

P2     J-l 

and  the  contraction  — 


Since  the  pressure  remains  constant  at  pz, 


Total  work  performed 


y-i 
Further — 

Therefore         Wx  +  W2  = 

For  practical  purposes  it  will  be  convenient  to  express 
p  in  atmospheres  and  v  in  ft.3,  when  the  result  will  be  in  ft.3 
atms.,  i  ft.3  atm.  *  representing  the  work  done  in  moving  a 

*  i  ft.3  atm.  =  28-317  x  io3  x  1-0132  x  io«  ergs 

=  2-8690  x  io10  ergs. 
i  K.W.H.  =  3'6  x  io8  watt  seconds 
=  3-6  x  io6  x  io7  ergs 
=  3-6  x  io13  ergs. 

/.  i  K.W.H.  =     3'6  X  IQl3,0  ft.3  atms. 

2-8690  X  IO'° 

=  1255  ft.8  atms. 
or     i  H.P.H.  =  1255  x  0-746  ft.3  atms.  =  936  ft.8  atms. 


INTRODUCTION  37 

piston  i  ft.2  in  area  through  i  ft.  against  ar  pressure 
difference  of  i  atm.  For  further  simplification,  take  p\=i 
atm.,  and  vl=iooo  ft.3.  Then — 

~* 
Wj+Wa^:  —  —  \(^r)      —i>  ft.3  atms. 

and  for  diatomic  gases — 

„,     ,  ATT        1000  X  i'4i(/^2\0'29        )  £±  ' 

Wi+W2=i 3±J(c?i     —if  ft.3  atms. 

0-41       \\fij  5 

IOOO  X  1^ 


As  an  example,  let  us  take  the  compression  of  1000  ft.3 
of  air  from  i  atm.  to  201  atms.,  starting  and  finishing  the 
operation  at  the  same  temperature,  e.g.  15°  C. 

Work  then  equals  — 

t  /orjT\°'29  "i 

3-674j(52£)       -  i  j  H.P.H.  =  13-4  H.P.H. 

It  is  interesting  to  see  the  effect  on  the  efficiency  of 
compressing  in  a  number  of  stages,  e.g.  consider  the  operation 
to  be  effected  in  three  stages,  the  pressure  in  each  phase 
rising  to  201*  times  (5*86  times)  the  starting  pressure  with 
intermediate  cooling  to  the  initial  temperature.  Thus, 
In  the  first  stage  the  pressure  rises  from  i  to  5-86  atms. 

second  „  „  „  „     5-86  „     34-3 

third  „  „  „  „    34-3     „   201*0       „ 

It  is  obvious  that  the  temperature  rise  in  each  stage 
will  be— 


Q'39 


Consequently  the  work  done  in  each  case  will  be  the  same 
and  equal  to  — 

3-674  (5-86°'29-  i)  H.P.H.  =-2-462  H.P.H. 


38  INDUSTRIAL    GASES 

while  the  total  work  of  compression  will  be  — 
3  X  2-462  H.P.H.  —7-386  H.P.H. 

The    general    form    of   the    expression    for    multi-stage 
compression,  where  n  =  the  number  of  stages,  is  — 


y  —  I 

or,  per  1000  ft.3  of  a  diatomic  gas  measured  at  i  atm. 
pressure  — 


0*29 


W=3'674»{@"    -ij  H.P.H. 

Isothermal  compression.  —  Consider  a  volume  of  gas  v\ 
at  pressure  pi  to  be  compressed  to  p2.  If  the  com- 
pression be  performed  in  such  a  way  that  the  heat  produced 
escapes  so  rapidly  that  no  increase  in  temperature  occurs, 
the  work  performed  is  given  by  the  expression  — 


W  = 


r 
\ 

J 


.dv 

v 


* 

assuming  Boyle's  L,aw  throughout. 

In  this  case  the  number  of  stages  has  no  influence,  and 
taking  again  the  case  of  1000  ft.3  of  gas  at  i  atm.  pressure 
to  be  raised  to  201  atms.  — 

W  =  1000  log,  aji  ft.3  atms. 
=  5300  ft.3  atms. 
=  WG-  H.P.H.  =  5-66  H.P.H. 

In  actual  practice,  with  large  multi-stage  (3—5)  com- 
pressors, the  overall  efficiency  allowing  for  friction  losses, 
etc.,  is  some  80  %  of  that  calculated  as  above  for  adiabatic 
compression. 


INTRODUCTION  39 

Thus,  with  three-stage  compression,  the  power  for  the 
compression  of  1000  ft.3  of  air  to  200  atmospheres  would 
be— 


JI  p  H  B.H.P.H. 

O'o 

equivalent  to  6*89  K.W.H. 

Allowing  for  an  efficiency  of,  say,  85  %  in  the  electric 
motor  driving  the  compressor,  the  actual  energy  expenditure 
would  be  8-n  K.W.H. 

The  power  demanded  in  practice  is  found  to  vary  from 
about  12  to  8  K.W.H.  per  1000  ft.3,  according  to  the  size 
of  the  plant. 

Notes  on  Compressed  Gases—  Safety  Precautions.— 
In  dealing  with  compressed  gases,  due  regard  should  be  paid 
to  the  question  of  the  strength  of  materials  and  to  the 
correct  engineering  design  of  the  containers  and  conduits 
employed.  In  fact,  an  elementary  knowledge  of  the  methods 
of  calculating  the  factors  of  safety  of  the  various  parts  of 
the  apparatus  used,  of  the  mechanical  properties  of  the 
steels  and  other  materials  used  in  the  construction  of  high- 
pressure  plant,  and  of  the  influence  of  mechanical  work  and 
heat  treatment  on  the  same  may  be  said  to  be  a  sine  qua 
non.  The  material  for  the  construction  of  the  weldless 
steel  cylinders  employed  for  the  commercial  transport  of 
compressed  gases  is  legally  defined  in  this  country  as  steel 
containing  not  more  than  0*25  %  carbon.  For  further 
details,  mechanical  tests,  etc.,  cf.  Recommendations  of  the 
Parliamentary  Committee  on  the  Manufacture  of  Compressed 
Gas  Cylinders,  1895. 

When  dealing  with  inflammable  gases,  it  is  very  important 
to  make  sure  by  analysis  that  oxygen  is  absent  from  the 
gases  undergoing  compression,  or  at  any  rate  is  present 
only  in  small  quantities  well  below  the  limit  of  inflamma- 
bility, since  the  momentary  temperature  rise  on  the  com- 
pression stroke  is  often  sufficient  to  cause  explosion  ;  similarly, 
it  is  important  that  the  compressor  should  be  specially 
designed  for  use  with  inflammable  gases,  i.e.  it  should  be 


40  'INDUSTRIAL   GASES 

of  the  enclosed  type — not  open,  as  in  the  ordinary  Whitehead 
"  liquid  air  "  compressor,  for  example. 

The  limits  between  which  explosion  is  possible  are  given 
below  for  a  number  of  gases.  The  values  are  for  atmo- 
spheric pressure. 

TABLE  5. 
EXPLOSIVE  LIMITS. 


Gas. 

Minimum  %  air  in  gas 
for  explosion. 

Minimum  %  gas  in 
air  for  explosion. 

Hydrogen     .  . 

25-8* 

0* 

Carbon  monoxide    . 

25-8* 

12-5* 

Methane 

. 

84-6* 

5-3* 

Coal  gas 

.  . 

79  t 

7t 

Blast  furnace  gas    . 

.  f 

35  t 

36  t 

Water  gas  (Bunte,  1901)    .  . 

33'25 

12-4 

With  electrolytic  gas  which  may  contain  oxygen  un- 
diluted by  nitrogen  the  limits  are  considerably  smaller 
(cf .  p .  202) .  Increased  pressure  appears  to  have  no  noteworthy 
effect  on  the  limits  of  inflammability  (cf .  Burrell  and  Ganger, 
loc.  cit.) .  Further  investigations  carried  out  by  Burrell  and 
Robertson  (Technical  Paper,  No.  121)  with  methane  show 
that  reduction  of  pressure  has  the  effect  of  narrowing  the 
explosive  limits ;  thus,  no  methane-air  mixture  will  ignite 
at  pressures  below  275  mm.  On  the  other  hand,  the  same 
investigators  found  that  in  the  case  of  methane  the  limits 
were  widened  by  increase  of  temperature ;  the  minimum 
percentage  of  methane  in  air  for  inflammation  is  lowered 
from  5*5  %  at  the  ordinary  temperature  to  375-4  %  at  500°  C. 

According  to  Terres  and  Plenz  (J.  Gasbeleucht.,  57, 
(1914),  990,  1001,  1016),  in  the  case  of  mixtures  of  rrydrogen, 
carbon  monoxide  and  methane  with  air,  the  effect  of  in- 
creased pressure  is  to  narrow  the  explosive  limits,  especially 
for  carbon  monoxide  mixtures,  the  upper  limit  of  methane 
being  an  exception.  Increase  of  temperature  widens  the 
limits. 

*  Coward,  Chem.  Soc.  Trans.,  (1914),  1859;  Coward,  Carpenter  and 
Payman,  Ib.,  (1919),  27. 

t  Burrell  and  Gauger,  Technical  Paper,  No.  150,  Bureau  of  Mines, 
U.S.A. 


INTRODUCTION  41 

A  propos  of  the  danger  of  explosion  from  the  possibility 
of  meeting  with  explosive  mixtures  in  cylinders  the  following 
precautions  are  desirable  in  the  manipulation  of  compressed 
gases  :— 

(1)  The  avoidance  of  sudden  opening  of  valves  leading 
to  gauges,  etc.     By  the  adiabatic  compression  of  the  first 
portion  of  gas,  sudden  opening  of  a  valve  may  raise  the 
temperature  to  the  ignition  point  and  a  similar  effect  may 
be  produced  by  friction  in  closing  a  valve,  or  by  the  presence 
of  finely  divided  iron,  etc. 

(2)  Consistent    analysis    of    the    contents    of    cylinders 
before    exposing    to    conditions   which    might   initiate    an 
explosion  while  still  under  high  pressure,  also  if  the  con- 
tents of  several  cylinders  are  to  be  mixed    under    high 
pressure. 

When  compression  of  an  inflammable  gas  is  performed 
the  compressed  gas  should  be  tested  for  the  presence  of  any 
oxygen  which  may  have  been  introduced  accidentally 
during  the  compression. 

In  order  to  avoid  any  confusion  and  to  guard  against  the 
possibility  of  such  disastrous  mistakes  as  the  filling  up  with 
oxygen  of  a  cylinder  partly  filled  with  an  inflammable  gas, 
or  vice  versa,  rigid  rules  are  observed  by  all  filling  works 
that  each  cylinder  shall  be  emptied  before  recharging  and 
that  all  cylinders  containing  inflammable  gases  shall  be 
fitted  with  left-handed  screw  connections ;  oxygen,  air, 
nitrogen,  etc.,  are  carried  in  cylinders  with  right-handed 
connections.  Further,  the  cylinders  are  painted  distinctive 
colours :  thus,  hydrogen  is  contained  in  red  cylinders,  oxygen 
in  black,  and  nitrogen  or  air  in  grey  cylinders.  To  guard 
against  the  possibility  of  deposits  from  coal  gas  and  the  like, 
cylinders  which  have  been  fitted  with  left-handed  valves 
are  always  annealed  before  being  fitted  with  right-handed 
valves.  All  cylinders,  of  course,  are  annealed  and  re-tested 
at  regular  intervals. 

For  a  discussion  of  the  results  of  carelessness  in  respect 
of  the  above-mentioned  precautions,  cf.  Wohler,  Z.  angew. 
Chem.,  30,  (1917),  174.  Manometers  and  the  like  should 


42  INDUSTRIAL    GASES 

be  provided  with  gas  checks,  i.e.  constrictions  to  minimize 
the  effect  of  sudden  admission  of  gas. 

(3)  The  insertion  of  explosion  traps,  e.g.  tubes  packed 
with  copper  gauze  or  steel  wool,  may  often  be  advisable  in 
cases  where  explosion  is  possible. 

Oxygen  is  a  dangerous  gas  to  compress  unless  proper 
precautions  are  taken,  while  manipulation  of  the  compressed 
gas  requires  care,  as  in  the  presence  of  oil,  etc.,  an  explosion 
is  easily  initiated  in  various  ways,  as  indicated  above.  All 
oxygen  pressure  gauges  and  connections  should  be  scrupu- 
lously free  from  oil  or  other  organic  matter,  and  only  water 
can  be  used  for  the  lubrication  of  the  compressors  (cf. 
Rasch,  Z.  fur  komp.  u.  fliissige  Gase,  (1904),  141).  Acetylene, 
being  an  endo thermic  compound,  is  very  dangerous  to 
compress  by  reason  of  its  liability  to  detonate. 

It  has  been  observed  in  the  rapid  release  of  compressed 
hydrogen  that  ignition  occasionally  occurs.  The  origin  of 
the  phenomenon  is  somewhat  uncertain;  possible  sources 
avre  electrical  sparks  due  to  dust  disturbed  from  the  valve, 
etc.,  or  the  catalytic  or  pyrophoric  action  of  finely  divided 
iron  oxide  or  metal  present  in  the  cylinder  or  valve  passages. 

A  feature  of  compressed  gases  which  should  be  borne 
in  mind  is  the  almost  complete  dryness  of  a  gas  at,  say, 
100  atmospheres  pressure.  Thus,  at  15°  C.  the  percentage 
of  water  vapour  will  be  about — 

12*8  x  100 

—P per  cent.  =  0*017  per  cent. 

760  x  ioo  * 

as  compared  with  a  possible  ioo  times  this  amount  at  the 
ordinary  pressure. 

Cylinders  of  compressed  gas  should  be  kept  in  a  cool 
place  as  a  rise  in  temperature  of,  say,  20°  C.  would  raise  the 
pressure  from  the  normal  value  of  120  atms.  to  some  128  atms, 

Liquefied  gases. — Reference  has  been  made  to  the  necessity 
of  keeping  cylinders  of  compressed  gases  cool ;  much  more 
does  this  consideration  apply  to  cylinders  containing  liquefied 
gases,  especially  if  the  cylinders  have  been  somewhat  over- 
charged with  liquid.  The  following  table,  adapted  from 


INTRODUCTION 


43 


Teichmann,  Komprimierte  und  verflussigte  Gase,  1908,  shows 
the  way  in  which  the  sensitivity  to  warming  varies  with  the 
degree  of  filling. 

The  figures  are  based  on  Regnault's  vapour-pressure 
measurements  (cf.  Table  7).  The  "normal  fillings"  are 
those  given  in  the  third  column  and  are  according  to  German 
regulations. 

TABLE  6. 

RELATION  BETWEEN  DEGREE  OF  FILLING  AND  PRESSURE  IN  CYLINDERS 
CONTAINING  LIQUEFIED  GASES. 


Gas. 

Volume  of  i  kilo,  of 
liquid  at  15°  C. 

Minimum  cylinder 
space  per  kilo,  of 
liquid  (litres). 

Absolute  pressure  (atms.)  exerted  at  temperatures  given  (°C.). 

Normal  filling. 

5  %  over-filling. 

10  %  over-filling. 

0 

10 

20 

3<> 

40 

o 

10 

20 

30 

40 

o 

10 

20 

30 

40 

Sulphur 
dioxide 
Carbon 
dioxide 
Nitrous 
oxide 

0-716 

I'230 
I'2O5 

0-8 
i'34 
i'34 

i'53 
35'4 
36-1 

2-26 
46*0 
44'8 

3*24 
588 
55'4 

4*52 

98-5 
79-8 

6*15 
138 
126 

i'53 
34'4 
36-1 

2*26 
46*0 
44'8 

3'24 
66'4 
55'4 

4'  52 
no 

99'  5 

6-15 
151 
152 

i'53 
35'4 
36-1 

2'26 

46  o 
44-8 

3-24 
76-6 
68-1 

13  at 
23-9°  C. 

I2O 
I2O 

162 
177 

The  rises  in  pressure  are  greater  than  the  vapour  pressures 
of  the  respective  liquids  at  the  temperatures  in  question,  as 
is  seen  from  the  following  table  : — 

TABLE   7. 
VAPOUR  PRESSURES  OF  LIQUEFIED  GASES. 


Absolute  vapour  pressure  (atms.)  at  temperature  given. 

Gas. 

o°C. 

10°  C. 

20°  C. 

30°  C. 

40°  C. 

Sulphur  dioxide  { 

r52 
l'$l 

2*26 
2'35 

324 

3'3° 

4'52 
4-60 

6-15 

6'20 

Regnault,  1862. 
Pictet,  1885. 

Carbon  dioxide    | 

35'4 
34'3 

46*0 
44-2 

58-8 
56-3 

73'8 
70-7 

91*0 

Regnault,  1862. 
Amagat,  1892. 

Nitrous  oxide  .  .  < 

36-1 
30-8 

44-8 

55'3 
49*4 

68-0 

83-4 

Regnault,  1862. 
Villard,  1897. 

Note. — At  40°  C.  both  carbon  dioxide  and  nitrous  oxide 
are  above  their  critical  temperatures.  The  difference  is 
due  to  the  bottle  becoming  filled  with  liquid,  of  course,  and 


44 


INDUSTRIAL    GASES 


the  temperature  at  which  this  would  occur  at  the  above 
cited  degrees  of  filling  is  given  in  the  following  table 
(Teichmann,  loc.  cit.) : — 

TABLE   8. 


Gas. 

Temperature  (°C.)  at  which  completely  full  with 

normal  filling, 
i.e.  as  in 
column  3, 
Table  6. 

5  per  cent, 
over-filling. 

10  per  cent, 
over-filling. 

Sulphur  dioxide 
Carbon  dioxide 
Nitrous  oxide 

64-6 
21*2 
24'9 

45'3 
18-1 
20-5 

23-2 
I4'2 
I6'I 

In  the  case  of  carbon  dioxide,  the  question  is  discussed 
very  fully  by  Stewart  (Trans.  Amer.  Soc.  Mech.  Eng.,  30, 
(1908),  mi),  according  to  whom  the  temperature  at  which 
the  cylinder  becomes  completely  filled  with  liquid  is  connected 
with  the  amount  of  the  charge  as  follows  :— 

TABLE  9. 


Cylinder  volume  in  litres  per  kilo. 

carbon  dioxide 

1-8 

r6 

1*4 

I'2 

Temperature  at  which  the  cylinder 

becomes  full.     °C. 

30-31 

28-30 

26 

15-20 

An  allowance  of  about  1*6  litres/kilo,  carbon  dioxide 
(or  39  lbs./ft.3)  is  recommended  by  Stewart  as  a  result  of 
his  calculations  and  experiments. 

As  the  cylinder  becomes  full  of  liquid  the  pressure  rise 
becomes  much  steeper,  although  the  rate  of  increase  is  of 
a  different  order  from  that  obtaining  with  water,  for  example. 
When  the  liquid  gas  is  very  near  its  critical  temperature, 
e.g.  carbon  dioxide,  Tc=3i'i°  C.,  the  coefficient  of  expansion 
becomes  relatively  very  large,  but  the  compressibility  also 
increases,  causing  the  pressure  curve  to  be  less  steep  than 
might  have  been  expected. 

In  this  country  the  recommendation  of  the  Parliamentary 
Committee  on  the  Manufacture  of  Compressed  Gas  Cylinders, 


INTRODUCTION 


45 


1895,  is  that  the  charge  of  carbon  dioxide  shall  not  exceed 
0*75  Ib.  per  Ib.  of  water  capacity,  while  a  figure  of  f  Ib.  is 
given  for  tropical  use,  corresponding  to  46*9  and  41*7  lbs./ft.3 
respectively  ;  for  ammonia,  0*5  Ib.  per  Ib.  of  water  capacity 
is  recommended  as  a  maximum  ;  no  specific  recommendations 
are  made  for  sulphur  dioxide  and  nitrous  oxide.  The 
Committee  recommends  attest  pressure  of  224  atms.  for  the 
cylinders  in  the  case  of  carbon  dioxide ;  attention  is  drawn  to 
the  regulations  in  force  on  the  German  railways,  given  below — 

TABLE   10. 
GERMAN  RAILWAY  REGULATIONS  FOR  CYLINDERS  OF  LIQUEFIED  GASES. 


Gas. 

Minimum  cylinder 
volume  per  kilo, 
(litres). 

Test  pressure 
(atms.). 

Carbon  dioxide 

J<34 

250 

Nitrous  oxide 

250 

Ammonia 

r86* 

100 

Chlorine 

0-9 

50 

Sulphur  dioxide 

0-8 

30 

Phosgene 

0-8 

30 

In  the  filling  of  cylinders  with  liquid  gases  the  complete 
exclusion  of  air  is  important,  since  the  presence  of  a  permanent 
gas  has  a  considerable  effect  on  the  pressure  set  up  in  the 
cylinder. 

When  sampling  liquefied  gases  the  sample  is  best  taken 
with  the  cylinder  in  an  inverted  position,  using  a  fine 
regulation  valve  ;  either  liquid  or  gas  can  thus  be  withdrawn 
without  contamination  with  any  air  which  may  be  present 
in  the  space  above  the  liquid  ;  compare,  however,  remarks 
relating  to  nitrous  oxide  on  pp.  289,  290. 

Heat-Interchange. — The  cost  of  nearly  all  technical 
operations  depends  on  the  fuel  consumption  which,  in  turn, 
is  determined  by  the  operations  of  heating  or  cooling  to 
which  the  gases,  or  their  parent  substances  or  products,  are 
subjected.  In  almost  all  cases  the  final  temperature  is 
the  same  as  the  initial  temperature,  i.e.  that  of  the  atmo- 
sphere, and  therefore,  apart  from  heat  usefully  employed  in 

*  2'o  litres/kilo,  recommended  by  British  Committee. 


46  INDUSTRIAL    GASES 

effecting   endothermic  reactions,   the  heat  is  theoretically 
capable  of  regeneration. 

It  will  therefore  be  well  to  examine  now  the  factors 
which  influence  the  transfer  of  heat  between  gases  and 
gases  (through  a  partition)  or  between  gases  and  solids. 

Suppose  one  to  require  a  knowledge  of  the  rate  of  transfer 
of  heat  per  unit  surface  per  degree  C.  temperature  difference 
per  unit  of  time  over  a  very  short  length  of  tube,  and  also  of 
the  relation  between  this  quantity  and  the  linear  velocity  of 
a  gas,  initially  at  a  temperature  tlt  passing  through  a  metal 
tube  the  outer  surface  of  which  is  maintained  at  a  lower 
temperature,  t2. 

The  rate  of  transfer  does  not  depend,  to  any  great 
extent,  on  the  thermal  conductivity  of  the  metal  tube  as 
might  at  first  be  thought,  the  gas  itself  offering  so  much 
resistance  to  heat  flow  that  the  resistance  of  the  metal  is 
almost  negligible  in  comparison.  If  the  gas  be  flowing  with 
stream-line  motion,  the  rate  of  transfer  will  be  very  low  indeed, 
since  it  can  only  occur  by  conduction  from  layer  to  layer  of 
the  gas,  and  gases  are  very  poor  conductors  of  heat. 

When,  however,  the  critical  velocity  is  exceeded,  we 
have  an  approach  to  temperature  equilibration  across  the 
bore  of  the  pipe ;  but,  although  very  much  better,  the  heat 
transference  still  falls  far  short  of  that  which  is  possible, 
as  far  as  the  thermal  conductivity  of  the  walls  is  concerned. 
This  is  due  to  a  stagnant  film  of  gas  on  the  walls  of  the 
conduit.  The  effect  of  increased  linear  velocity  is  to 
decrease  mechanically  the  thickness  of  this  film  with  con- 
sequent increase  in  the  value  of  the  heat  transfer  coefficient. 

According  to  Porter  (Trans.  Institution  of  Engineers 
and  Shipbuilders  in  Scotland,  Nov.  19,  1918),  following 
Osborne  Reynolds,  the  coefficient  of  heat  transfer  from  a 
given  fluid  to  the  walls  of  the  tube  through  which  it  is 
flowing  (or  vice  versa)  for  turbulent  motion  may  be  expressed 
in  general  terms  as  follows  :— 

K=MC/^Y    >~2 


INTRODUCTION  47 

where  K  =>  the  coefficient  of  heat  transfer, 

C  ==>  the  thermal  conductivity  of  the  fluid, 

v  =»  mean  linear  velocity  of  the  fluid, 

p  =•  density  of  the  fluid, 

[j,  =3  viscosity  of  the  fluid, 

d  =  diameter  of  the  tube, 

M  =3  a  constant, 
all  in  absolute  units. 

Since  a  survey  of  experimental  measurements  indicates 
that  n  may  be  taken  as  about  i'75,  the  equation  becomes  — 


The  main  inferences  to  be  drawn  from  this  relation  are  — 

(1)  The  heat  transfer  coefficient  will  vary  as  the  0*75 
power  of  the  linear  velocity. 

(2)  Except    for  stream-line  motion,   the  thermal  con- 
ductivity of  the  fluid  is  not  of  itself  the  determining  factor 
as  regards  heat  interchange  ;    thus,  although  hydrogen  has 
a   high   thermal  conductivity   as   compared   with   air,    its 
density  is  relatively  small,  while  the  viscosit)^  is  about  half 
that  of  air.     The  relative  values  are  seen  to  be  in  the  ratio  — 


Kair         CairVair     [ 

for  turbulent  motion,  and  equal  values  of  v  and  d  — 

^41-65  x  i  o~5/o  -000089873  x  I73  x  io—  6\°'75 
3  5'67"X  lo-5  \  0-0012928  X  86  X  io~6  / 
ato°C.  =1-68 

(3)  The  coefficient  of  transmission  will  slowly  fall  off 
as  the  diameter  of  the  tube  increases,  thus,  an  increase  in 
diameter  from  i  to  6  inches  with  otherwise  unchanged 
conditions  of  linear  velocity,  etc.,  results  in  the  decrease  in 
the  coefficient  in  the  ratio  of  — 


In  an  investigation  with  water,  Stanton  (Phil.  Trans.,  A, 
(1897),  67)  found  the  index  of  the  power  of  d  to  be  O'i6). 


48  INDUSTRIAL   GASES 

(4)  The  coefficient  will  increase  rapidly  with  increase 
in  the  pressure  of  the  gas,  since  the  density  is  approxi- 
mately proportional  to  the  pressure,  while  the  viscosity  and 
thermal  conductivity  *  are  almost  independent  of  pressure. 
Thus  one  would  expect  the  coefficient  for  a  pressure  of  100 
atms.  to  be  some  ioi*=>  32  times  that  at  atmospheric  pressure 
for  equal  linear  velocity. 

Further,  since  in  regard  to  pressure  variations — 
K  oc  (Vp)f  oc  (PV)* 

where  P  =  pressure  and  V  =  volume,  it  is  evident  that  K 
will  be  practically  constant  for  all  pressures,  provided  that 
vp  or  PV  is  constant,  i.e.  provided  that  the  quantity  of  gas 
flowing  through  the  conduit  in  unit  time  remains  the  same. 

The  above  considerations  apply  equally  to  liquids ; 
the  values  of  the  coefficient,  however,  are  much  higher, 
namely  of  the  order  of  several  hundred  times  those  observed 
with  gases  at  atmospheric  pressure  for  equal  linear  velocity. 
It  will  be  found  convenient  to  express  the  coefficient  K  in 
terms  of  C.H.U./ft.2/hr./°C.  temperature  differenced 

There  are  three  principal  types  of  heat  transfer,  as  regards 
gases,  to  be  considered — 

(1)  Heat  passes  from  a  gas  to  a  solid,  or  vice  versa.     Here 
we  need  to  consider  the  heat  transfer  coefficient  for  one 
gas  film  only. 

(2)  Heat  passes  from  a  gas  through  a  thin  metal  partition 
to  a  liquid,  or  vice  versa.     In  this  case,  let — 

kg  =3  the  coefficient  of  transfer  between  gas  and  metal  for 

the  rate  of  flow  obtaining, 
kw  =>  the    coefficient  of   heat    transfer  between  liquid  and 

metal  for  the  rate  of  flow  obtaining. 

Then  K  = 


neglecting  the  effect  of  the  tube  itself. 

*  The  thermal  conductivity  of  a  gas  may  be  expressed  as  r6o^Cv,  and, 
since  the  viscosity  and  specific  heats  are  not  greatly  affected  by  changes 
of  pressure,  the  thermal  conductivity  may  be  taken  as  approximately 
constant 


INTRODUCTION  49 

A  little  consideration  will  show  that  it  is  almost  correct 
to  neglect  kw  and  to  take  the  coefficient  of  the  gas  alone, 
this  being  the  determining  factor.  An  example  of  this  type 
of  interchange  is  the  cooling  of  air  by  passing  over  cold 
brine  pipes. 

(3)  Heat  passes  from  one  gas  through  a  thin  metal 
partition  to  another  gas.  - 

This  is  the  state  of  affairs  in  the  usual  gas  heat-inter- 
changer,  e.g.  in  the  B.A.M.A.G.  continuous  catalytic  process 
for  the  production  of  hydrogen  (p.  161).  In  such  a  case 
the  coefficient — 


will  be  of  the  order  of  half  the  value  of  kgi  or  kSz  if  these 
are  fairly  similar,  i.e.  if  similar  conditions  of  motion  and 
pressure  obtain  in  both  gas  currents. 

If,  however,  one  gas  be  at  a  high  pressure  and  the  other 
at  atmospheric  pressure,  as,  for  example,  in  a  liquid  air 
machine  heat-interchanger,  the  conditions  will  resemble 
those  in  case  (2),  the  low  pressure  gas  determining  the 
situation  although  the  coefficient  of  heat  exchange  between 
the  compressed  gas  at,  say,  100  atmospheres  pressure, 
and  the  metal  is  of  the  order  of  30  times  that  obtaining  in 
the  case  of  the  low  pressure  gas  for  similar  conditions  of 
motion. 

A  propos  of  the  investigation  of  existing  plant  and  the 
design  of  new,  it  is  important  to  note  that  the  mean  tem- 
perature difference  is  not  the  mean  of  the  initial  and  final 
temperature  differences,  except  in  the  case  of  a  heat- 
interchanger  with  counter-current  flows  of  equal  thermal 
capacities,  when  the  temperature  gradient  is  constant.  The 
mean  temperature  gradient  may  be  calculated  for  all  cases 
as  follows  :  — 


A. 


50  INDUSTRIAL  GASES. 

where  ^  =  the  temperature  difference  at  one  end  of  the  heat 

transfer  process, 

t2  »=i  the  temperature  difference  at  the  other  end  of  the 
heat  transfer  process. 

Some  values  due  to  Josse  are  given  by  Hausbrand 
("  Verdampfen,  Kondensieren  und  Kiihlen,"  Berlin,  Fiinfte 
Auflage,  1912)  for  air  at  a  pressure  of  1*034  alms,  traversing 
a  pipe  0*9  in.  diameter,  the  outside  of  which  was  kept  at 
100°  C.  by  steam.  Since  saturated  steam  gives  a  high 
coefficient  of  heat  transfer,  the  values  may  be  taken  as 
applicable  to  a  single  air  film.  The  values  are  adapted 
from  a  smoothed  curve. 


TABLE   ii. 
HEAT- INTERCHANGE  COEFFICIENTS  FOR  AIR  (SINGLE  FILM). 


Mean  linear  velocity  of  air  in  ft. /sec. 
K.  in  C.H.U./ft.*/hr./0  C 


1-6 


2-9 


20 


30 
6-8 


8-5 


50 
9-9 


60 
n'2 


The  relation  between  K  and  the  linear  -velocity  is 
approximately  that  given  on  p.  47. 

NOTE. — The  calculated  critical  velocity  for  this  case  is 
about  5  ft. /sec. 

Desiccation  of  Gases. — It  is  often  necessary  to  carry 
out  the  operation  of  desiccation  on  large  quantities  of  gas. 
Thus,  all  the  air  which  enters  an  air  liquefaction  plant  must 
be  scrupulously  dried  and  similarly  with  the  gases  for  the 
manufacture  of  hydrogen  by  the  L,inde-Frank-Caro  process 
(cf.  p.  172).  In  both  cases,  as  will  be  described  later,  the 
desired  effect  is  best  secured  by  refrigeration. 

A  less  obvious  example  of  need  for  desiccation  is  that 
of  the  air  supplied  to  blast  furnaces,  the  reason  lying  in 
the  endothermic  nature  of  the  reaction  between  water 
vapour  and  carbon.  The  water  present  in  the  air  at  15°  C., 
if,  say,  75  %  saturated  (vapour  pressure  of  water  at  15°  C. 
being  12 '8  mm.) 


INTRODUCTION  51 

• 

I2'8  X  075  X  100 
^  -  '  -  per  cent.  =  1*26  per  cent. 

by  volume  of  the  air,  or  6*0  %  of  the  oxygen  present. 

The  heating  effects,  assuming  combustion  to  carbon 
monoxide  only,  are — 

H2O  +  C  =>  CO  +  H2  —  29-1  kilo,  calories, 
2C  +  O2  =»  2CO  +  58  kilo,  calories. 

Heating  effect  of  100  gram-molecules  of  oxygen  =>  5800  K. 
Cooling      ,,       ,,       6          ,,         „         „    water  vapour 

=>  174*6  K. 

But  coke  consumed  is  equivalent  to  103  gram-molecules 
of  oxygen  which  would  have  given  5974  K. 

Th      r         heat  actually  produced      5800  — 174*6 
possible  heat  production  ~          5974 

« §6253  ao/o 

5974 

So  far  we  have  considered  only  the  number  of  heat 
units  produced  from  a  given  weight  of  coke  without  reference 
to  the  efficiency  of  their  utilization.  In  actual  practice, 
the  economy  effected  is  considerably  greater  than  that 
represented  by  the  above  comparison,  amounting  to  a 
saving  of  the  order  of  30  %  of  the  fuel  required  per  ton  of 
iron  produced.  The  reason  for  this  fact  probably  lies  in 
the  greater  ease  of  reduction  due  to  the  higher  temperature 
attained  and  possibly  to  the  different  equilibria  established 
in  the  furnace  in  the  absence  of  water  vapour,  also  in  the 
greater  regularity  of  operation. 

The  most  practical  way  of  effecting  the  dehydration 
(first  carried  out  on  the  large  scale  by  Gay  ley  (Trans.  Amer. 
Inst.  of  Mining  Engineers,  35,  (1904),  746  ;  36,  (1905),  3*5) 
in  America,  plants  having  been  installed  also  in  this  country) 
is  to  cool  the  air  to  a  temperature  of  about  —  5°  C.  by  means 
of  ammonia  refrigeration  machines.  For  the  most  economical 
working,  the  bulk  of  the  water  is  separated  above  o°  C.  in 


52  INDUSTRIAL  GASES 

order  to  avoid  the  energy  demanded  by  the  absorption  of 
the  latent  heat  of  solidification.  The  vapour  pressure  at 
— 5°  C.  is  about  3  mm.,  i.e.  the  percentage  of  water  vapour 
left  in  the  air, 

0-395%  by  volume. 

A  heat-inter  changer  is  used,  of  course,  to  minimize  the  power 
expenditure. 

An  alternative  method  is  to  pass  the  air  up  a  tower, 
down  which  cooled,  concentrated  calcium  chloride  liquor 
is  sprayed ;  the  weakened  liquor  is  re-concentrated,  re- 
frigerated and  returned  to  the  system  (cf.  Chem.  Trade  ]., 
62,  (1918),  113).  Besides  that  of  diminished  fuel  con- 
sumption, the  drying  has  further  advantages,  such  as  the 
decreased  air  blast  required  and  diminution  in  the  dust 
present  in  the  exit  gases ;  but  the  high  cost  of  the  cooling 
plant  must  be  taken  into  consideration  in  computing  the 
economics  of  air  desiccation. 

The  Storage  of  Gas. — In  most  operations  relating  to 
gases,  it  is  necessary  to  store  considerable  quantities  of  gas 
to  serve  as  a  balance  against  irregular  operation  of  the  gas- 
producing  plant,  or  variable  demand,  as  in  the  case  of  coal 
gas.  In  such  cases  it  is  usual  to  store  the  gas  in  holders 
consisting  of  a  bell  or  a  series  of  bells  rising  and  falling  in  a 
water  seal.  Such  gas  holders  have  been  constructed  up  to 
a  capacity  of  about  17  million  ft. 3.  It  is,  however,  sometimes 
convenient  to  store  gas  at  a  pressure  of  about  20  atmospheres 
in  cylindrical  vessels  of  about  3  in.  diameter,  while  similar 
vessels  are  used  for  railway  transit. 

Reference  Data. — In  the  following  tables  will  be  found 
collected  data  which  are  useful  in  connection  with  technical 
gas  problems.  The  data  for  the  table  of  physical  constants 
have  been  selected  from  the  best  modern  determinations. 


INTRODUCTION 


53 


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54 


INDUSTRIAL  GASES 


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INTRODUCTION 


55 


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Solubility  in  water  at 
15°  C.  C.c.  of  gas  at 
N.T.P.  in  i  c.c.  water 
at  i  atm.  pressure,  (A) 
including,  (B)  exclud- 
ing water  vapour. 


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INDUSTRIAL  GASES 


TABLE   13. 


Heat  of  combustion.    C.H.U. 

per  looo  ft.3  at  15°  C. 

Heat  of  formation. 
C.H.U.  per  Ib.mol. 

Coefficient  of 
expansion  of  the 
liquid. 

Net. 

Gross. 

Ozone 

X  I03 

68-0 

Hydrogen 

153,300 

l8l,2OO 

— 

— 

Carbon  monoxide 

180,500 

— 

(      29  from 
\  amorphous  C. 

— 

Carbon  dioxide    .  . 

— 

— 

(     97'3  from    f 
\  amorphous  C.\ 

15°  C.  O'OIOI2 
20°  C.  0*01308 

Sulphur  dioxide  .  . 

— 

— 

(      70  from       f!  15°  C.  0*00186 
\  rhombic  S.    \\  20"  C.  ©'00192 

Nitrous  oxide 

:  — 

— 

—  19'5       { 

15*  C.  0-00852 

20*  C.  0-OIII2 

Methane 

506,000 

562,000 

|     2  1  '7  from 
\  amorphous  C. 

— 

TABLE   14. 
USEFUL  CONVERSION  FACTORS. 


inch 
metre 
ooo  ft.3 
m.3 
m.3 
gallon 
in.3 
Ib. 

gram. 

atmosphere 
C.H.U. 
ft.3  atm. 
K.W.H. 
K.W.H. 
K.W.H. 
H.P.H. 
H.P.H. 
H.PH. 
Ib.  coal 
Ib.  coke 
0-25^,/KW.H, 


2*5400  cm. 
3-281  ft. 
28*317  m.3 

35  3i  ft.8 
220*0  gallons. 
4-5460  litres. 
16*387  cm.3 
453-6  grams. 
15-432  grains. 
14-690  lbs./in.2 
1-800  B.T.U. 
1-511  C.H.U. 
1255  ft.3  atms. 
860-2  kilo,  calories, 
1896  C.H.U. 
0-746  K.W.H. 
936*0  ft.3  atms. 
1415  C.H.U. 
about  7000  C.H.U. 
about  8000  C.H.U. 
Years. 


REFERENCES. 

General  Theory. — Travers,  "  The  Experimental  Study  of  Gases."    London, 

1901. 

Chwolson,  "  Traits  de  Physique."    Paris,  1906-13. 
Haber,  "  Thermodynamics  of  Technical  Gas  Reactions."   London,  1908. 
Nernst,    "  Experimental    and    Theoretical   Applications   of  Thermo- 
dynamics to  Chemistry."    London,  1907. 
Gas  Analysis. — Lunge,  "  Technical  Gas  Analysis."     London,  1914. 


INTRODUCTION  57 

Heat  Transfer. — Hausbrand,  "  Verdampfen,  Kondensieren  und   Kiihlen." 

Berlin,  Fiinfte  Auflage,  1912. 

Physical  Constants. — The  values  in  the  table  are  partly  selected  from 
Landolt-Bornstein-Roth,  "  Physikalisch-Chemische  Tabellen." 
Berlin,  Vierte  Auflage,  1912,  and  from  Kaye  and  Laby,  "  Physical 
and  Chemical  Constants,"  London,  Third  Edition,  1918.  Many 
values,  however,  are  taken  from  the  original  sources,  and  special 
reference  may  be  made  to  the  following : — 

Specific  Heats  of  Oxygen,   Nitrogen  and  Hydrogen  at   Constant 
Pressure : 

Scheel  and  Heuse,  Annalen   [4],  40,  (1913)  473,  492;  Escher, 

Annalen,  [4],  42,  (1913),  761. 
Specific  Heats  of  Nitrogen  and  Carbon  Dioxide  at  Constant  Volume  : 

Crofts,  Chem.  Soc.  Trans.,  (1915),  290. 

Critical  Temperatures  and  Pressures  of  Oxygen,  Nitrogen,  Hydro- 
gen, Carbon  Monoxide  and  Methane : 

Cardoso,  /.  Chim.  Phys.,  13,  (1912),  312 ;  Bulle,  Physikal.  Zeits., 

14,  (1913),  860. 
Thermal  Conductivity : 

Weber,  Annalen,  [4!,  54,  (1917),  325.  437- 
Boiling  and  Melting  Points : 

Table  of  melting  points  and  standard  temperatures  issued  by 
the  American  Bureau  of    Standards,   /.  Soc.    Chem.    Ind., 
(1919),  67  R. 
General     References. — Thorpe,   "  A  Dictionary   of    Applied   Chemistry." 

London,  1912. 

Martin,  "  Industrial  Gases."     London,  1916. 

Roscoe  and  Schorlemmer,  "  Treatise  on  Chemistry."     London,  1911. 
Molinari,  "  Treatise  on  General  and  Industrial  Chemistry,"  vol.  i., 
Inorg.  (Feilmann).     London,  1912. 


PART  I. —THE  GASES  OF  THE  ATMOSPHERE 
SECTION  I. — AIR 

Properties  of  Air. — In  view  of  the  complex  nature  of  air 
it  is  not  proposed  to  enter,  at  this  stage,  into  a  discussion 
of  its  properties,  as  these  are  best  defined  by  a  consideration 
of  the  following  sections ;  the  more  important  physical 
constants  will  be  found  in  Table  12,  pp.  53-5. 

According  to  Holborn  and  Austin  (Sitzungsber .  Kgl. 
Preuss.  Akad.  Wiss.,  (1905),  175),  the  mean  specific  heat  at 
constant  pressure  varies  with  temperature  as  follows  : — 


Temperature  °  C. 

S 

20-440 
20-630 
20-800 

0-2366 
0-2429 
0-2430 

According  to  Witkowski,  the  mean  value  of  C^,  between 
—  102°  C.  and  17°  C.  is  0*2372. 

The  influence  of  pressure  over  the  range  1-300  atms.  on 
the  specific  heat  is  seen  from  the  formula  given  by  Holborn 
and  Jakob  (Z.  Verein.  deut.  Ing.,  61,  (1917),  146)  for  a 
temperature  of  60°  C. — 

io4Cj  =»  2414  +  2'86p  +  o'ooo^p2  —  o'ooooio6/>3 

p  being  in  atmospheres. 

Composition  of  the  Atmosphere.— The  composition  of 
the  atmosphere  is  not  absolutely  constant,  but  the  following 
table  will  serve  to  indicate  the  general  composition,  according 
to  the  most  recent  experiments.  It  is  obvious  that  the 


AIR  59 

atmosphere  is  by  no  means  such  a  simple  mixture  as  is 
sometimes  imagined. 

TABLE    15. 
COMPOSITION  OF  THE  ATMOSPHERE. 

Component.  Percentage  (by  volume). 

Nitrogen        , .          . .          . .          . .          . .          •  •  78*05 

Oxygen          .  .          . .          . .          . .          . .          . .  2i"o 

Argon             .  .          .  .          .1          0-93236 

Neon  .  .          .  .          .  .          .  .          .  .          . .          . .  0-00181 

Helium          0-00054 

Krypton        . .          . .          . .          . .          •  •          •  •  0-0000049 

Xenon            0*00000059 

Carbon  dioxide         . .          . .          . .          . .          . .  0-03-0-3 

Hydrogen      . .          . .          . .          . .          . .          . .  0*019  * 

Methane        0-0121  * 

C6H6  and  similar  hydrocarbons    . .          . .          . .  0*0017  * 

Carbon  monoxide,  together  with  hydrocarbons  of 

the  type  CwH2w_2  and  CnH2M     .  .         '. .          . .  0-0002  * 

Formaldehyde          0-002-0-005 

Ozone  . .          . .          .  .          . .          . .          . . \ 

Hydrogen  peroxide  . .          . .          . .          . .  I 


Ammonia      ..          .  Variable  traces 

Nitric  acid,  oxides  of  nitrogen 

Sulphur  compounds 

Chlorine  compounds 

Water  vapour  . .          . .          . .          . .          . .       Variable 


iiJ 


The  percentage  of  oxygen  is  not  quite  constant,  but 
varies  slightly  according  to  the  locality  and  the  altitude ; 
the  maximum  variations  being  of  the  order  of  0*1  %.  The 
carbon  dioxide  content  is  usually  about  0*03  %,  rising  to 
some  two  or  three  times  this  value  in  towns  during  fogs, 
while  in  badly  ventilated  rooms  the  concentration  may  rise 
to  about  0-3  %. 

In  this  connection  it  is  interesting  to  note  that  the 
composition  of  exhaled  air  is  somewhat  as  follows  :— 

Per  cent. 

Nitrogen       . .          79*1 

Oxygen          . .          . .          . .         . .       16*5 

Carbon  dioxide        . .          . .          . .         4 '4 

TOO'O 

*  The  values  marked  with  an  asterisk  are  due  to  Gautier  (Annales  de 
Chim.  et  de  Phys.,  [7],  22,  (1901),  5).  Rayleigh  gives  a  lower  value  for 
hydrogen,  viz.  0-003  %.  The  presence  of  the  oxygen-nitrogen  compounds 
is  probably  due  to  electrical  action,  while  the  sulphur  compounds  are 
mostly  derived  from  household  and  industrial  contamination.  A  certain 
amount  of  sodium  chloride  is  to  be  found  in  suspension  in  the  atmosphere 
in  the  neighbourhood  of  the  coast. 


6o  INDUSTRIAL  GASES 

The  Liquefaction  of  the  Permanent  Gases  (Air). 

The  liquefaction  of  permanent  gases  is  a  subject  which 
claimed  the  attention  of  scientists  and  inventors  for  many 
years  before  any  degree  of  success  was  attained. 

A  permanent  gas  is  distinguished  from  a  vapour  in  that 
the  critical  temperature  of  the  former  is  below  the  ordinary 
temperature,  that  of  the  latter  above.  With  gases  of  the 
latter  category,  of  which  sulphur  dioxide  and  carbon  dioxide 
may  be  taken  as  representative  examples,  the  mere  applica- 
tion of  sufficient  pressure  at  the  ordinary  temperature  is 
all  that  is  required  to  produce  liquefaction.  When  one 
considers  that  the  critical  temperatures  of  nitrogen  and 
oxygen  are  —145°  C.  and  — 118°  C.  respectively  (as  was 
subsequently  discovered) ,  the  difficulties  encountered  by  the 
early  experimenters  are  not  surprising.  Progress  was 
facilitated  by  Cailletet's  discovery,  in  1877,  of  the  principle 
of  cooling  by  adiabatic  expansion  through  the  (accidental) 
sudden  expansion  of  compressed  acetylene  in  a  glass  tube, 
with  the  momentary  formation  of  a  mist.  Repetition  with 
oxygen  and  nitrogen  (at  a  pressure  of  200  atmospheres)  and 
even  with  hydrogen  (at  300  atmospheres),  employing  a 
constant  external  temperature  of  — 28°  C.,  yielded  a  similar 
result. 

The  cooling  effect  of  adiabatic  expansion  is  expressed 
by  the  formula — 


Although  of  great  scientific  interest,  these  brilliant 
experiments  contributed  but  little  to  the  practical  solution 
of  the  problem  of  liquefying  permanent  gases  in  bulk. 
Some  further  progress  was  made  by  Pictet,  the  so-called 
"  cascade  "  method  being  employed.  Carbon  dioxide  was 
first  liquefied  under  slight  pressure  at  a  temperature  of 
—65°  C.,  produced  by  the  ebullition  of  liquefied  sulphur 
dioxide  under  reduced  pressure.  The  carbon  dioxide  was 
in  turn  evaporated  under  diminished  pressure,  yielding  a 


AIR  61 

temperature  of  —130°  C.,  and  was  then  used  to  cool  a  tube 
supplied  with  oxygen  at  a  pressure  of  some  300  atmospheres. 
On  opening  the  exit  valve  a  transient  stream  of  liquid  was 
observed  ;  here  again  the  yields  were  very  minute.  By  the 
evaporation  of  liquid  ethylene,  care  being  taken  to  provide 
efficient  thermal  insulation,  Olszewski  and  Wroblewski,  in 
1885,  obtained  a  temperature  of  —152°  C.,  at  which  tempera- 
ture both  oxygen  and  nitrogen  were  liquefied  under  pressures 
in  the  neighbourhood  of  25  atms.  The  cascade  method 
was  elaborated  further  by  Kammerlingh  Onnes,  using, 
(i)  methyl  chloride,  (2)  ethylene,  and  (3)  oxygen.  By  the 
evaporation  of  the  oxygen  under  reduced  pressure  a  tempera- 
ture of  —200°  C.,was  reached  and,  finally,  —270°  C.  was 
realized  by  the  addition  of  (4)  a  helium  system. 

The  problem  of  producing  liquid  air  technically  was 
solved  almost  simultaneously  by  Hampson  in  England 
(B.P.  10165/95),  lyinde  in  Germany  (B.P.  12528/95),  and 
by  Tripler  in  America  (B.P.  15235/99).  All  these  investi- 
gators made  use  of  the  Joule-Thomson  Effect  (cf.  p.  10),  in 
conjunction  with  the  principle  of  the  heat-interchanger  first 
propounded  by  Siemens  in  1857. 

This  effect  is  not  to  be  confused  with  the  adiabatic 
expansion  of  a  gas  performing  external  work  ;  the  fall  in 
temperature  being  mainly  due  to  the  internal  work  involved 
in  the  separation  of  the  molecules. 

The  approximate  fall  in  temperature  in  the  case  of  air 
can  be  evaluated  from  the  expression  — 


*T  =  0-276^  ~P2)  degrees  C. 

where  pi  and  p2  are  the  initial  and  final  pressures  respec- 
tively, when^  is  not  far  removed  from  atmospheric  pressure. 

When  this  property  of  imperfect  gases  is  utilized  in 
conjunction  with  the  principle  of  heat-interchange  one 
obtains  a  progressive  fall  in  the  temperature  of  the  expanded 
air  until  the  point  of  liquefaction  is  reached. 

Theory  of  Cooling  by  the  Joule-Thomson  Effect.— 
Some  reference  to  the  Joule-Thomson  Effect  has  been  made 


62 


INDUSTRIAL  GASES 


on  p.  10  in  the  Introduction,  but  a  more  complete  exami- 
nation will  be  necessary  for  a  thorough  understanding  of 
air  on  liquefaction  processes. 

Consider  a  volume  of  gas  v0  under  a  pressure  of  pQ  atmo- 
spheres at  an  (absolute)  temperature  of  T0.  L,et  the  gas  be 
compressed  to  a  higher  pressure  pi  at  a  temperature  Tx 
(the  volume  becoming  Vj).  Imagine  the  compressed  gas 
at  pressure  pi  to  be  disposed  in  a  cylinder  A  (Fig.  5),  closed 
by  a  frictionless  piston  B,  which  is  kept  in  position  by 
another  frictionless  piston  F  of  suitable  area  exposed  to  a 


FIG.  5.  —  Production  of  cold  by  the  Joule-Thomson  Effect. 

constant  pressure  p2  on  the  side  marked  H  (e.g.  in  contact 
with  the  atmosphere),  the  space  B  being  vacuous.  By 
means  of  the  valve  C  the  gas  is  allowed  to  expand  to  pressure 
p2  into  the  cylinder  D,  closed  by  a  frictionless  piston  G 
working  against  a  pressure  p2.  We  will  suppose,  further, 
that  any  temperature  change  which  may  occur  on  expansion 
is  rectified  in  the  course  of  passage  through  the  connecting 
tube  so  that  the  whole  operation  is  isothermal. 

Now  the  work  performed  by  the  gas  on  the  piston 
Q^p2V2,  while  that  performed  by  the  piston  B  on  the  gas 
(=  work  performed  by  the  gas  at  H  on  the  piston  F) 


*  In  actual  practice,  this  work  p^v^  is  performed  by  the  piston  of  the 
compressor  in  addition  to  that  demanded  by  the  actual  compression  of 
the  gas.  Since,  however,  the  compressor  is  fed  with  gas  at  pressure  p2, 
the  power  absorbed  by  the  compressor  is  approximately  equal  to  that 
calculated  on  pp.  34-9. 


AIR  63 

Since  most  gases  show  a  greater  or  less  deviation  from 
Boyle's  Law,  p\v\  is  not  necessarily  equal  to  ptfJ^,  and  the 
work  performed  by  the  system  on  the  external  gas  at 
pressure  p%  (which  will  generally  be  one  atmosphere) 


~H.e  representing  the  cooling  (or,  if  negative,  the  heating) 
produced  by  external  work.  In  addition,  we  have  to  consider 
the  internal  work  due  to  the  separation  of  the  molecules, 
which  will,  in  all  cases,  operate  in  the  direction  of  producing 
a  cooling  effect  (Ht-). 


f- 

v* 

J  vt 


when  a  is  the  constant  representing  the  cohesion  of  the 
molecules  in  Van  der  Waals'  equation— 


Now   a   may   be   derived   from   the   following   relation 
(cf.  p.  7)  :— 

27 

Tc  and  pc  being  the  critical  temperature  and  pressure 
respectively.  Thus,  in  the  case  of  air,  if  we  take  as  units 
cubic  feet  and  atmospheres  and  consider  a  volume  of  1000  ft.8 
measured  at  i  atm.  pressure  and  15°  C.,  i.e.  pQ  =>  i,  ^0=1000, 
TO  -288, 

„_    27 


64  X  39V  288 
We  will  now  consider  the  cooling  effect  in  C.H.U. 
(cf.  p.  12)  of  an  expansion  of  this  mass  of  air  from  200  atms. 
(absolute)  to  i  atm.  at  a  temperature  of  15°  C.,  assuming 
the  temperature  to  be  kept  constant  by  external  supply  or 
abstraction  of  heat. 

Now  for  15°  C.  and  i  atm.    pQvQ  =>p2v2  =*  IOO° 

1000  X  1*0855 


200 


1.0587 

1025-3 


64  INDUSTRIAL  GASES 


=>  1000  —  1025*3  ft.3  alms. 

="-  253  X  1-511  C.H.U.  * 

=--38-23  C.H.U. 

H,  is  seen  to  be  negative,  consequently  a  heating  effect  will 
be  produced  if  the  external  work  alone  be  considered. 

_ 


/I025'3  \ 

2307  ( —  —  1000  ) 

=  -          V  20° I  ft.3  atms. 

1025-3  X  1000 

200 

^2307X994-87  ft  3  atms.  =4477  ft.3  atms. 
5126-5 

=.447-7  X  1-511  C.H.U. 
=•676-5  C.H.U. 
.-.  .total  cooling  effect  =  676 -5  —  38-2  C.H.U. 

-3  638 -3  C.H.U. 

Since  the  specific  heat  at  constant  pressure  of  air  at  15°  C. 
is  equivalent  to  18-5  C.H.U./iooo  ft.3/0  C.,  this  cooling  is 
equivalent  to  a  fall  in  temperature  of — 


This  agrees  sufficiently  well  with  the  values  experi- 
mentally determined  by  Bradley  and  Hale  (Phys.  Review, 
29,  (1909),  258),  who,  for  a  pressure  drop  from  204  atms.  to 
i  atm.  at  o°  C.,  found  a  temperature  fall  of  44*6°  C. ;  especially 
as  their  more  favourable  conditions  would  give  a  greater 
cooling  effect  to  the  extent  of  about  5°  C. 

As  the  compression  of  1000  ft.3  of  air  at  15°  C.  to  200  atms. 
requires  in  practice  a  power  expenditure  of  the  order  of 
10  K.W.H.  (cf.  p.  39),  the  cooling  effect  per  K.W.H. 
power  expenditure  is  638-3/10  =  63*83  C.H.U. 

*  i  ft.8  atm.  =  2*8690  x  io10  ergs.  (cf.  p.  36) 
i  C.H.U.  =  453-6  gram  calories 

=  453*6  x  4-185  X  io7  ergs 

=  1*8983  x  io10  ergs. 
/.  i  ft.8  atm.  =  2-8690/1-8983  C.H.U. 

=  1-511  C.H.U. 


AIR  65 

Expansion  at  —  100°  C.  —  We  will  next  consider  the  effect 
of  performing  the  above  isothermal  expansion  after  a 
preliminary  cooling  of  the  compressed  gas  to,  say,  —  103°  C., 
down  to  which  temperature  the  pv  values  have  been  deter- 
mined by  Witkowski  (loc.  cit.,  cf.  Table  2,  p.  6).  This  is 
about  the  temperature  to  which  the  air  is  cooled  before 
expansion  in  the  simple  type  of  machine  such  as  the  Hampson 
plant  (cf.  Bradley  and  Hale,  Physical  Review,  19,  (1904), 
391)  ;  the  temperature  does  not  fall  below  the  critical 
temperature  and,  consequently,  no  liquefaction  occurs 
before  expansion. 

As  Witkowski's  experiments  were  not  extended  to 
pressures  exceeding  130  atms.,  we  will  take  the  values  at 
this  pressure. 

Considering,  as  before,  1000.  ft.3  of  air  at  15°  C.  and 
i  atm.  (in  these  calculations  Witkowski's  values  are  multi- 
plied by  273/288,  since  pQvQ  is  taken  at  15°  C.) 

for  15°  C.  and  i  atm.      pQv0  =>  1000 

—  103-5°  C.    »     i     »         ^a  =  587-9 
-103-5°  C.    ,,130,,         ^i=>  377-4 
We  have  thus  a  very  considerable  deviation  from  per- 
fection, the  gas  being  now  more  compressible  than  a  perfect 
gas  ;  consequently  H,  will  be  positive. 

H,  ="#»»t  —  P\VI  =>  587'9  —  377*4  ft.3  atms. 

=  210-5  ft.3  atms.  ==•  318-1  C.H.U. 

2307(3^-587.9) 
_  a(vi  _  Vz}  7V  I3Q        )      JJ 


377-4  X  587-9 
130 

^  2307  X  585-0  ft  3  atms. 
I706-7 

=>  791  ft.3  atms.  =  1195  C.H.U. 
Total  cooling  effect,  therefore, 

=>  1195  +  318-1  C.H.U.  =*  1513  C.H.U. 
A  similar  calculation   for  the  expansion  of   the  same 
quantity  of  air  from  130  atms.  to  i  atm.  at  a  temperature 
A.  5 


66  INDUSTRIAL  GASES 

of  15°  C.  gives  a  corresponding  cooling  effect  of  470  C.H.U. 
(H.  -  15-4  C.H.U. ;  H,  =  454'3  C.H.U.) 

The  cooling  effect  is  thus  found  to  be  considerably 
greater  at  the  lower  temperature. 

Turning  to  the  actual  practical  operation  of  liquid  air 
plants,  it  should  be  noted  that  the  above  observed  difference 
of  1513  —  470  C.H.U.  (=  1043  C.H.U.)  is  not  usefully  avail- 
able for  the  production  of  liquid  air,  since  the  additional 
cooling  effect  is  balanced  exactly  by  the  extra  heat  evolution 
in  the  heat-inter  changer  of  the  incoming  gas  ;  this  prevents 
the  temperature  of  the  compressed  gas  arriving  at  the 
expansion  valve  from  falling  below  about  — 100°  C.  The 
additional  cooling  is  absorbed  in  lowering  the  temperature 
of  the  expanded  gas  to  that  at  which  the  cold  gas  enters  the 
interchanger,  viz.  the  boiling  point  of  air.  It  would  only 
be  available  if  the  compressor  were  operated  at  the  same 
temperature  of  — 103°  C.  Consequently,  the  value  of  pv  at 
the  temperature  of  entry  of  the  compressed  gas  into  the 
interchanger,  or,  more  strictly,  the  difference  between  the 
values  of  pv  for  the  gases  entering  and  leaving  the  inter- 
changer respectively,  assuming  the  heat-interchange  to  be 
perfect,  determines  the  amount  of  cooling  produced.  Since 
the  heat-interchange  is  not  perfect  the  heat  required  to  heat 
up  the  exit  gases  to  the  inlet  temperature  must  be  deducted 
from  the  cooling  effect. 

We  shall  see  later  the  effect  of  a  preliminary  pre-cooling 
of  the  gas. 

The  heat  evolution  of  the  incoming  compressed  gas, 
alluded  to  above,  has  the  effect  of  making  the  temperature 
gradient  between  the  two  fluids  in  the  heat-interchanger 
increase  as  the  temperature  falls.  Obviously,  the  growing 
imperfection  of  the  compressed  gas  will  be  accompanied 
by  an  increase  in  the  specific  heat,  the  effect  being  very 
marked  near  the  critical  temperature  at  high  pressures. 

The  outcome  of  the  above  considerations  is,  that  we  get 
the  same  cooling  effect  with  a  low  temperature  expansion, 
accompanied  by  a  considerable  fall  in  temperature,  as  in 
the  example  given  above,  in  which  a  temperature  of  15°  C. 


AIR  67 

and  isothermicity  were  assumed.  Consequently,  we  may 
take  the  cooling  effect  under  actual  working  conditions  as 
being  of  the  order  of  638  C.H.U.  for  a  working  pressure  of 
200  atmospheres. 

When  liquefaction  sets  in  the  external  work  performed 
on  the  atmosphere  by  the  issuing  air  diminishes.  The 
decrease  is  compensated  for,  however,  by  the  absorption 
of  heat  due  to  external  work  performed  by  the  air  which 
escapes  liquefaction  on  the  portion  liquefied. 

We  have  already  seen  that  the  power  expenditure  is  of 
the  order  of  10  K.W.H.  per  1000  ft.3  of  air  compressed. 
Therefore,  cooling  effected  by  i  K.W.H.  (measured  on  the 
switchboard)  =  about  64  C.H.U.  ,  equivalent  to  the  pro- 
duction of  about  0-29  litre  of  liquid  air.  The  above 
estimate  is,  of  course,  based  on  the  (incorrect)  assumption 
that  there  are  no  thermal  losses  ;  the  efficiency  falls  off  in 
proportion  to  the  extent  of  such  leakages. 

Before  leaving  the  subject  it  will  be  worth  while  to  examine 
the  case  of  hydrogen,  which,  as  stated  above,  gives  a 
heating  effect  at  the  ordinary  temperature. 

The  case  of  Hydrogen.  —  Taking  1000  ft.3  of  hydrogen  at 
15°  C.  and  i  atm.  and,  after  compression  to  200  atms. 
(absolute),  expanding  to  i  atm.,  we  have  — 


H, 


1000  x  1*198  ,,  . 
=v   -V   =  1000  ---  -  ft3  atms. 


=  1000  —  1134  ft.3  atms. 

=  —  134  ft.3  atms.  =  —  202  C.H.U. 


27        /iooo  X  3i'95\2      taking  pe  as  equal 
/ 

4721  —  —  —  iooo  ) 


""64  X  ii'O\         288         /        to  11*0  atms. 
=  472 


1134  x  iooo 

200 


ft.3atms. 


=  472  X  994'3  ft3atms. 

5670 
=  82-8  ft.3  atms.  =  125  C.H.U. 


68  INDUSTRIAL  GASES 

Therefore  total  cooling  effect 

=  _  202  +  125  C.H.U.  =  -  77  C.H.U. 

Heating  effect  per  atm.  pressure  drop  =>  -= — — — —  °  C. 

18-20  X  199 

(since  specific  heat  =  18-20  C.H.U./iooo  ft.3/°C.) 

=  0-0213°  C. 

The  value  determined  experimentally  by  Joule  and 
Thomson  was  0*03°  C.  for  6*8°  C.  and  pressures  near  atmo- 
spheric ;  if  the  above  calculation  be  repeated  for  20  atms. 
the  value  obtained  is  0-018,  not  greatly  different  since  the 
pv  curve  is  practically  a  straight  line  between  i  and  200  atms. 

As  the  temperature  is  lowered,  H,  decreases  and  H^ 
increases  owing  to  the  growing  imperfection  of  the  gas, 
with  the  consequence  that  at  —80*5°  C.  an  inversion  point 
is  reached ;  below  this  temperature  a  cooling  effect  sets 
in,  but  is  not  very  marked  until  the  temperature  is  lowered 
to  the  neighbourhood  of  —200°  C.  It  is  found  necessary 
to  pre-cool  to  this  temperature  before  the  liquefaction  of 
hydrogen  can  be  effected  by  the  Joule-Thomson  effect. 
The  beneficial  influence  of  pre-cooling  will  be  discussed 
under  the  L,inde  process  of  air  liquefaction. 

The  final  improvement  in  the  liquefaction  of  permanent 
gases  was  suggested  by  Siemens,  while  its  technical  develop- 
ment is  due  to  Claude,  who  overcame  the  difficulties  of 
employing  expansion  accompanied  by  the  performance  of 
external  work.  With  this  system  of  working  it  is  important 
not  to  allow  the  temperature  to  fall  below  about  — 140°  C., 
as  the  increase  in  the  specific  heat,  in  conjunction  with  the 
diminished  amount  of  external  work  which  the  gas  is  capable 
of  performing  at  lower  temperatures  owing  to  its  rapidly 
increasing  compressibility,  leads  to  low  efficiencies.  A 
more  detailed  account  will  now  be  given  of  the  principal 
systems  of  making  liquid  air. 

As  regards  patents  relating  to  this  subject,  the  number 
is  so  great  and  the  differences  in  many  cases  so  involved 
that  it  is  impossible  in  the  present  volume  to  do  more  than 
give  a  resume  of  the  salient  features  of  those  which  have 
assumed  commercial  importance. 


AIR  69 

MANUFACTURE  OF  LIQUID  AIR 
Useful  Constants 

Weight  of  1000  ft.3  of  air  at  15°  C.  and  i  atm.  pressure 
=  76*49  Ibs. 

Weight  of  i  litre  of  liquid  air  =  about  i  kilo. 

Volume  of  i  litre  of  liquid  air  when  vaporized  =  about 
28  ft.s  at  15°  C.  and  i  atm. 

Heat  uiuts  which  must  be  abstracted  for  the  production 
of  i  litre  of  liquid  air  from  atmospheric  air  =  about 
220  C.H.U. 

Hampson  System 

The  Hampson  system  is  a  convenient  one  for  laboratory 
use,  being  usually  supplied  in  5  K.W.  sets  which  furnish 
about  i  litre  of  liquid  air  per  -hour,  equivalent  to  the  ab- 
straction of  about  44  C.H.U. /K.W.H.  Although  somewhat 
inefficient,  it  possesses  an  important  advantage  for  such 
experimental  purposes  in  its  simplicity.  Air  is  compressed 
to  175-200  atmospheres,  being  first  freed  from  carbon 
dioxide  by  passage  over  a  series  of  trays  filled  with  lime. 
After  depositing  the  lubrication  water  in  a  separator,  the 
gases  are  freed  from  residual  traces  of  carbon  dioxide  and 
water  vapour  in  a  purifier,  consisting  of  a  steel  cylinder 
charged  with  sticks  of  caustic  potash,  and  are  then  allowed 
to  expand  at  a  fine  adjustment  valve,  finally  flowing 
through  a  heat-interchanger  back  to  the  compressor. 

Some  5  %  of  the  compressed  air  is  liquefied  at  each  cycle 
when  the  apparatus  has  once  become  thoroughly  cooled 
down.  Complete  removal  of  the  carbon  dioxide  and  water 
vapour  is  important,  as  otherwise  blockages  may  occur  in 
the  liquefier.  Working  for  about  10  minutes  is  sufficient 
for  the  production  of  liquid  air  to  commence. 

The  apparatus,  as  made  up  by  the  British  Oxygen  Co., 
is  shown  in  Fig.  6.  The  compressed  air  entering  at  A 
traverses  the  heat-interchanger  coils  B,  and  undergoes 
expansion  at  the  valve  C,  which  is  adjusted  by  the  hand 
wheel  B.  After  expansion,  the  air  passes  over  the  coils,  its 
path  being  determined  by  baffles,  to  the  outlet  F.  The  level 


INDUSTRIAL   GASES 


of  the  liquid  in  the  receiver,  which  holds  some  100  c.c.,  is 
indicated  by  the  glycerol  gauge  H ;  the  liquid  air  is  periodically 
withdrawn  by  the  valve  T.  A  thick  layer  of  lagging,  e.g. 
sheeps'  wool,  is  disposed  around  the  central  portion. 


Linde  System 

The  Ivinde  system  (cf. 
B.P.  14111/02)  is  perhaps 
the  system  most  commonly 
used  in  large  scale  practice. 
It  differs  from  the  simple 
Hampson  process,  quite 
apart  from  constructional 
details.  In  the  first  place, 
instead  of  expanding  the 
air  from  200  atms.  to  i 
atm.,  I/inde  expands  only 
from  200  atms.  to  .  about 
50  atms.  We  will  ex- 
amine the  diminution  in 
the  cooling  effect  as  com- 


FIG.  6. — Hampson  Liquefier  (British  Oxygen  Co.). 

pared  with  the  decrease  in  the  power  expenditure. 

We  have  seen  that  with  an  expansion  from  200  atms. 


AIR  71 

(absolute)  to  i  atm.,  the  cooling  is  of  the  order  of  638  C.H.U. 
for  the  expansion  of  1000  ft.3  of  air  measured  at  15°  C.  and 
i  atm.  In  the  present  case — 

p^i  =  1025-3  at  200  atms.  and  15°  C. 
p2v2  =   983-3  at    50  atms.  and  15°  C. 

Therefore      H,  =  (^2^2)^5  —  (Pivi)i5 

—  983-3  — 1025-3  ft-3  atms. 

=  -  42  ft.3  atms.  =  -63-5  C.H.U. 


aW1025'3 

^  2QO  _          ft>3  atms. 
1025-3  x  983-3 


200  X  50 
=  2307  X  I4-542-  X  10,000  ft  3 

1025-3  x  983-3 

=  3327  ft.3  atms.  =  502-7  C.H.U. 

Total  cooling  effect  =  502-7  —  63-5  C.H.U. 
=  439-2  C.H.U. 

The  ratio  of  the  above  cooling  to  that  obtained  with  the 
full  expansion  to  i  atm.  =  439/638  =  1/1*45.  The  power 
expenditure  will  also  be  lower,  as  follows. 

Assuming  the  compression  to  be  adiabatic,  the  power 
varies  as  — 

0*29 


(cf.  p.  38).  In  the  present  case  we  have  :  (i)  single  stage 
compression  of  ^th  of  the  air  from  i  to  50  atms.  (since 
about  xoth  of  the  air  is  liquefied  in  each  cycle)  ;  (2)  single 
stage  compression  of  the  whole  of  the  air  from  50  to  200  atms. 
(absolute). 

In  the  straightforward  case  we  have  compression  of  the 
whole  of  the  air  from  i  to  200  atms.  (absolute)  in,  say,  two 
stages  (in  large  installations  three-stage  compressors  are 
usually  employed). 


72  INDUSTRIAL  GASES 

The  ratio  of  the  power  expenditures  will  be  — 


5o/  3     o-i  x  2-11+0-495 


2XI"56 


"3-28 

Consequently,  the  ratio  of  output  to  power  expenditure  is 
increased  by  the  Linde  system  of  working  in  the  proportion 
of  3-28/1-45  =2-26/1. 

Effect  of  Pre-cooling.  —  Another  improvement  intro- 
duced by  lyinde  consisted  in  the  pre-cooling  of  the  gas  fed  into 
the  interchanger  to,  say,  —  35°  C.,  by  means  of  an  ammonia 
refrigeration  system.  As  referred  to  above,  the  enhanced 
cooling  effect  produced  by  effecting  the  expansion  at  low 
temperatures  is  counteracted  by  the  fact  that  the  compressed 
gas  arrives  at  the  expansion  valve  at  a  temperature  con- 
siderably above  that  of  the  cold  gas  entering  the  heat- 
interchanger.  In  other  words,  the  thermal  capacity  of  the 
compressed  gas  over  the  temperature  range  in  question 
is  much  greater  than  that  of  the  same  volume  of  expanded 
gas.  When  liquefaction  is  in  progress  the  cold  air  enters 
the  regenerator  at  a  fixed  temperature,  viz.  that  of  the 
boiling  liquid  air  ;  consequently  the  temperature  at  which 
the  compressed  gas  reaches  the  expansion  valve  will  be 
determined  by  the  temperature  at  which  it  enters  the 
interchanger,  as  well  as  by  the  degree  of  perfection  of  the 
interchanger. 

If,  therefore,  the  incoming  compressed  air,  after  being 
slightly  cooled  by  the  interchanger,  be  diverted  therefrom, 
cooled  to,  say,  —30°  C.,  by  means  of  an  ammonia  or  other 
system,  and  subsequently  returned  to  the  interchanger, 
the  temperature  of  the  gas  arriving  at  the  expansion  valve 
will  be  lowered  by  an  amount  corresponding  to  the  heat 
units  abstracted  by  the  auxiliary  cooling  plant.  In  con- 
sequence, an  increased  yield  of  liquid  air  will  result.  The 
exact  procedure  may  be  seen  by  reference  to  Fig.  7. 


AIR 


73 


FIG.  7. — Linde 
System. 


It  should  be  pointed  out  that  the  re- 
frigeration effected  by  an  ammonia  system 
is  much  more  economical  than  that  pro- 
duced by  the  Joule-Thomson  effect, 
although,  of  course,  the  practical  lower 
limit  is  in  the  neighbourhood  of  —35°  C.  ; 
at  this  temperature  the  cooling  effected  is 
of  the  order  of  1000-2000  C.H.U./K,W.H., 
as  compared  with  60-180  C.H.U./K.W.H. 
by  the  Joule-Thomson  effect.  As  a  result 
of  the  p re-cooling  the  efficiency  of  the 
process  is  raised  by  some  30  per  cent. 

The  combined  effect  of  these  two 
modifications  is  approximately  to  treble 
the  production  of  liquid  air  per  K.W.H., 
this  being  equivalent  to  about  0*87 
litres/K.W.H.,  taking  the  previously  calcu- 
lated value  of  0-29  litres/K.W.H.  for  the 
single  cycle  and  neglecting  thermal  leakage, 
etc.  In  actual  practice,  0-65  litres/K.W.H. 
is  about  the  production. 

I^inde  machines  on  the  above  lines  are 
made  in  different  sizes,  from  the  laboratory 
type  with  a  production  of  some  075  litre/hr. 
upwards.  In  large  plants  three-stage 
compressors  are  used  and  the  compressed 
air,  after  separation  of  the  lubrication 
water,  is  completely  dried  by  cooling  with 


74 


INDUSTRIAL  GASES 


an  ammonia  refrigeration  system  to  about  —25°  C.,  using 
duplicate  cooling  systems,  which  are  periodically  changed 
over  (three  or  more  times  weekly)  in  order  to  allow  the 
deposited  ice  to  thaw  out.  Before  compression,  the  carbon 
dioxide  is  removed  by  means  of  towers  fed  with  caustic 
soda  solution.  Traces  of  carbon  dioxide  are  usually  formed 
during  the  compression  by  the  action  of  the  air,  heated 
by  the  adiabatic  compression,  on  the  packings  of  the  pump. 

The  diagrammatic  representation,  Fig.  7,  indicates  the 
course  of  the  compressed  air.  Passing  from  the  compressor 
A,  through  the  water  separator  B,  and  the  preliminary  heat- 
interchanger  C,  to  one  or  other  of  the  ammonia  coolers  D 
and  D1,  the  dry  gas  enters  the  liquefier  through  the  triple 
heat-interchanger  B.  (The  actual  interchanger  consists  of 
concentric  spiral  tubes.) 

Arriving  at  the  valve  F,  expansion  to  about  50  atmo- 
spheres takes  place,  the  gas  being  returned  to  the  last  stage 
of  the  compressor.  The  air  liquefied  in  the  separator  G, 
under  a  pressure  of  50  atms.,  is  allowed  to  expand  to  ordinary 
pressure  through  the  valve  H,  suffering  thereby  partial 
evaporation  ;  the  gaseous  fraction  returns  to  the  inlet  of 
the  compressor  through  the  interchanger  K.  Liquid  air 
is  drawn  off  from  the  vessel  I.  The  smaller  sizes  of  plant, 
up  to  about  3  litres/hr.  capacity,  are  fitted  with  two-stage 
compressors,  in  which  case  the  expansion  is  from  200  atms. 
to  about  20  atms. 

The  outputs  and  efficiencies  of  various  sizes  of  plants 
are  indicated  in  the  following  table  : — 

TABLE    16. 
LINDE  LIQUID  AIR  PLANTS. 


Litres  of  liquid  air  per  hour  with 

pre-cooling 

°'75 

5 

20 

5° 

100 

Litres  of  liquid  air  per  hour  with- 

out pre-cooling 

— 

— 

I2'5 

35 

70 

Power  K.W.  (measured  on   the 

switchboard) 

2'6 

14-2 

39 

78 

142 

Litres/K.W.H.  with  pre-cooling 

0*29 

°'35 

0-51 

0^64 

0-70 

Litres/K.W.H.  without  pre-cool- 

ing           

— 

— 

0-32 

o'45 

0-49 

Cooling  water,  gallons/hour 

55 

308 

835 

1760 

3300 

AIR  75 


Claude  System 

The  Claude  system,  as  above  indicated,  depends  on  the 
cooling  effect  produced  by  expansion  accompanied  by 
external  work,  together  with  that  due  to  internal  work, 
the  latter  being,  however,  small  compared  with  the  former. 
Usually  the  working  pressure  does  not  exceed  40  atmo- 
spheres. The  useful  temperature  limit  which  is  reached  by 
such  expansion  of  compressed  air  in  an  engine  cylinder  is 
about  —140°  C.,  and  much  of  the  initial  difficulty  in  the 
working  out  of  the  process  was  due  to  this  fact. 

On  account  of  the  rapidly  increasing  imperfection  of 
the  air  at  this  temperature  in  the  direction  of  greater 
compressibility,  expansion  at  a  lower  temperature  is  accom- 
panied by  relatively  little  work,  the  cooling  effect  produced 
by  which  may  be  balanced  by  the  friction  of  the  machine. 
This  temperature  is,  however,  about  the  critical  temperature 
of  air  (Tc  =  —140°  C.  ;  pc  =  39  atms.)  ;  consequently,  by 
using  the  expanded  gas  to  cool  a  receptacle  supplied  at 
40  atms.  pressure  with  air  which  has  been  pre-cooled  in  a 
temperature-interchanger,  liquefaction  of  the  high  pressure 
air  ensues  (B.P.  27658/02).  On  release  to  the  ordinary 
pressure,  partial  evaporation  occurs  and  the  temperature 
falls  to  — 190°  C.  By  adjusting  the  height  of  the  liquid 
in  the  liquefier-temperature-interchanger,  and  consequently 
the  rate  of  liquefaction,  the  air  arrives  at  the  expansion 
engine  at  a  temperature  of  about  — 100°  C. 

Considerable  trouble  was  at  first  experienced  in  the 
lubrication  of  the  expansion  cylinder,  ordinary  petrol  being 
employed ;  but  recently  it  has  been  found  that  suitably 
treated  leathers  can  be  used  without  any  lubrication. 

By  the  Claude  system,  an  output  of  about  075  litre  of 
liquid  air  per  K.W.H.  (measured  on  the  switchboard)  is 
claimed.  The  general  method  of  working  may  be  explained 
further  by  reference  to  the  diagrammatic  representation, 
Fig.  8.  Compressed  air,  at  about  40  atms.  pressure,  enters 
through  the  heat-inter  changer  M,  and  suffers  expansion 


76 


INDUSTRIAL  GASES 


in  the  cylinder  D,  the  engine  being  coupled,  either  mechani- 
cally or  electrically,  to  the  compressor.  The  cold  expanded 
gases  pass  round  the  tubes  of  the  second  inter  changer  I/, 
and  cause  the  liquefaction  of  the  compressed  air  supplied 
to  the  inside  of  the  tubes,  and  finally  leave  through  the 
interchanger  M.  The  liquid  air  collects  in  the  header  at 
the  bottom  of  the  tubes  and  is  drawn  off  in  accordance  with 
the  temperature  of  the  gas  arriving  at  the  expansion  engine. 


FIG.  8. — Claude  Liquefaction  System. 
(Claude's  "  Liquid  Air,  Oxygen  and  Nitrogen.") 

A  modification  of  this  plan  consists  in  effecting  the 
expansion  in  two  stages ;  in  the  first,  the  pre-cooled  air  is 
expanded  in  the  cylinder,  35  (Fig.  9),  so  as  to  produce  a 
temperature,  e.g.  — 160°  C.,  well  below  the  critical  tempera- 
ture. After  producing  the  liquefaction  of  the  compressed 
air  in  the  temperature-interchanger,  24,  26,  being  warmed 
to  from  — 130°  to  — 140°  C.  in  the  process,  the  air  undergoes 
a  further  expansion  in  36,  and  in  turn  serves  to  liquefy  the 
air  in  a  second  interchanger,  25,  27. 

To  avoid  leaks  of  the  very  cold  air,  the  two  cylinders 
are  arranged  in  tandem,  only  the  low  pressure  cylinder 
having  a  stuffing  box.  It  is  claimed  that  a  production  of 
0*9  litre/K.W.H.  (measured  on  the  switchboard)  is  attained 
in  a  moderately  large  plant. 


AIR 


77 


The  low  working  pressure  and  the  rapidity  in 'starting 
up  of  the  Claude  plant  are  both  in  its  favour,  and  the 
general  tendency  of  late  years  has  been  to  instal  Claude 


FIG.  9. — Claude  Liquefaction  System. 

rather    than    L,inde    plants.      The    following    table    gives 
particulars  of  a  few  sizes  of  Claude  plants  : — 

TABLE   17. 
CLAUDE  LIQUID  AIR  PLANTS. 


Production,  litres/hr. 

5 

50 

65 

Power  (measured  on  the  switchboard)  K.W.H.* 

H 

56 

70 

Litres  of  liquid  air  per  K.W.H. 

0-36 

0-89 

0-93 

With  reference  to  the  possible  effect  of  accumulations 
of  solid  argon,  methane  or  acetylene  in  causing  explosions 
in  liquid  air  plants,  cf.  Bramkamp  (/.  Soc.  Chem.  Ind., 
(1914),  240). 

Properties  of  Liquid  Air. — Liquid  air  is  a  mobile  liquid 
with  a  pale  blue  colour,  varying  in  intensity  according  to 

*  According  to  Mewes  (Z.fur  Sauerstoff  und  Stickstoff  Industrie,  5,  (1913), 
317),  the  power  figures  given  by  Linde  are  the  gross  values  read  off  on  the 
switchboard,  while  Claude's  figures  apply  to  the  power  on  the  compressor 
shaft.  Claude's  figures  have  therefore  been  increased  by  25  per  cent., 
assuming  80  per  cent,  efficiency  in  the  motor. 


78  INDUSTRIAL  GASES 

the  oxygen  content.  Its  density  is  about  1*0  and  the 
boiling  point  varies  from  —183°  to  —196°  C.,  according  to 
composition  (cf.  p.  80). 

Freshly  liquefied  air  usually  contains  considerably 
more  than  21  %  of  oxygen,  e.g.  50-60  % ;  on  standing, 
the  oxygen  content  increases.  The  specific  heat  is  about 
0*5,  while  the  latent  heat  of  vaporization  is  about  50  calories 
per  gram  (i.e.  per  c.c.)  =  50  C.H.U./lb.  On  cooling  liquid 
air,  nitrogen  separates  out  at  about  — 213°  C.  in  a  compara- 
tively pure  state ;  the  oxygen  does  not  solidify  until  a 
temperature  of  —225°  C.  is  reached. 

Liquid  air  has  feeble  magnetic  properties  on  account  of 
its  oxygen  content.  Its  refractive  index  (/AD)  is  1*2062. 
On  mixing  equivalent  quantities  of  liquid  nitrogen  and 
oxygen,  a  contraction  of  about  J  %  is  observed,  accompanied 
by  a  temperature  rise  of  about  0*5°  C. 

Applications  of  Liquid  Air. — The  principal  application 
of  liquid  air  is  in  the  manufacture  of  oxygen  and  nitrogen 
by  fractionation.  At  the  time  of  its  first  discovery,  many 
fantastical  claims  were  made  for  its  application  as  a  source 
of  power,  etc.,  but  apart  from  the  above,  no  very  extensive 
use  has  been  made  of  liquid  air.  A  considerable  advance 
in  the  possibility  of  the  industrial  use  is  due  to  the  perfection 
of  the  metal  vacuum  vessel.  Liquid  air  can  be  purchased 
(at  about  55.  per  gallon)  in  metal  vessels  holding  up  to 
about  five  gallons.  These  vessels  are  on  the  lines  of  the  glass 
Dewar  vessel,  being  furnished  with  a  charcoal  tube  cooled 
by  the  liquid  air,  for  the  purpose  of  effecting  the  complete 
exhaustion  of  the  jacket.  For  a  discussion  of  certain 
explosions  originating  from  the  accidental  breaking  of 
liquid  air  vessels  and  the  consequent  contact  of  the  contents 
with  the  charcoal,  cf.  Wohler,  Chem.  Zeit.,  Oct.  5,  1918. 
Liability  to  explode  under  these  conditions  is  considered  to 
depend  on  the  presence  of  catalysts,  such  as  iron  oxide,  in  a 
highly  absorptive  charcoal. 

Liquid  air  of  about  60  %  oxygen  content  is  used  in  mine 
rescue  apparatus,  some  five  litres  of  liquid  air  being  contained, 
absorbed  in  asbestos  wool,  in  a  vessel  with  only  moderate 


AIR  79 

thermal  insulation  (kieselguhr)  ;  a  slow  evaporation  results 
which  supplies  a  stream  of  air  to  the  breathing  apparatus. 
The  advantages  over  the  similar  apparatus  employing 
compressed  oxygen,  are  the  comparative  lightness  (the 
weight  is  about  30  Ibs.),  length  of  action,  and  the  greater 
ease  of  manufacture  of  liquid  air,  as  compared  with  com- 
pressed oxygen,  at  the  pit-head. 

Numerous  proposals  have  been  made  with  regard  to 
the  use  of  liquid  air  in  conjunction  with  carbonaceous 
matter  or  aluminium  as  an  explosive.  The  usual  method 
of  application  is  to  employ  a  cardboard  cartridge  with  a 
perforated  inner  tube  ;  a  mixture  of  kieselguhr  and  oil,  or 
soot,  etc.,  is  inserted,  the  cartridge  placed  in  the  bore-hole 
and  liquid  air  injected,  after  which  the  charge  is  fired 
electrically.  This  method  was  used  in  cutting  the  Simplon 
Tunnel.  The  chief  advantages  claimed  are  the  absence  of 
fumes  and  the  lack  of  danger  in  case  of  a  misfire,  as  the  charge 
rapidly  becomes  innocuous.  On  the  other  hand,  the  necessity 
for  firing  very  rapidly  after  charging  and  the  difficulty  of 
transportation  and  storage  of  the  liquid  air  are  against  its 
general  application. 

Separation  of  the  Constituents  of  Liquid  Air- 
Theoretical  Considerations. — As  has  already  been  pointed 
out,  the  principal  application  of  liquid  air  is  in  the  pro- 
duction of  oxygen  and  nitrogen. 

The  separation  of  the  constituents  of  liquid  air  by 
fractionation  was  propounded  by  Parkinson  in  B.P.  4411/92, 
but  was  first  realized  by  Dewar. 

To  glance  first  at  the  theoretical  side  of  the  question, 
we  are  indebted  to  the  work  of  lyinde  and  to  the  more 
complete  investigation  of  Baly  (Phil.  Mag.,  49,  (1900),  517), 
for  the  relation  between  the  liquid  and  gaseous  phases  of 
nitrogen- oxygen  mixtures,  Fig.  10. 

The  curves  indicate  that  starting  with  liquid  air  of 
21  %  oxygen  content,  the  percentage  of  oxygen  in  the  first 
fraction  is  about  7  %,  rising  as  evaporation  proceeds.  It 
will  be  noticed  that  there  is  no  mixture  of  maximum  or 
minimum  boiling  point,  and  that,  consequently,  application 


8o 


INDUSTRIAL  GASES 


of  ordinary  fractionation  column  principles  should  result 
in  effective  separation  as  far  as  oxygen  is  concerned  ;  it  is, 
however,  impossible  by  simple  fractionation  to  reduce  the 
oxygen  content  of  the  nitrogen  fraction  to  below  7  %.  It  will 
be  seen  later  that  this  can  be  accomplished  by  special  means. 


DEGREES  CENTIGRADE 

-L  1 

D  00  0 
3  C/i  C 

^ 

/ 

>*  60  cb  cb 
w  o  w  o 

TEMPERATURE  (ABSOLUTE) 

^ 

i 

x 

/ 

x 

TEMPERATURES 

0  ' 

i  $  a 

/ 

/ 

X 

<^ 

^ 

'WW0        10      20      30     40       50       60      70      80      90      100 
PERCENTAGE  OF  OXYGEN 

PERCENTAGE  OF  OXYGEN 

FIG.  10. — Baly's  Curves  for  the  liquid  and  gaseous  phases  of  the  system 
nitrogen-oxygen  at  atmospheric  pressure. 

As  regards  the  minimum  energy  involved  in  the  separation, 
it  was  indicated  by  Parkinson  in  the  above  patent  that 
recuperation  of  the  cold  would  be  desirable,  in  which  case 
only  the  losses  in  the  heat-interchanger  are  involved,  apart 
from  the  energy  required  for  the  actual  separation  of  the 
gases,  a  factor  liable  to  be  overlooked.  This  latter  quantity 
corresponds  to  the  isothermal  compression  of  the  nitrogen 
to  079  of  its  original  volume  and  of  the  oxygen  to  0'2i  of  its 
volume,  i.e.  in  each  case — 


(cf.p.38) 


AIR  81 

Taking  for  example,  1000  ft.3  of  air  at  15°  C.  and  i  atm., 
the  work  involved  is — 

1000  X  079  X  2-3026  X  log  - 
+  1000  X  o-2i  X  2-3026  X  log  -    -  ft.3  atms. 

=  514-0  ft*  atms.  =^o  H.P.H. 

936-2 
=  0-549  H.P.H.  per  1000  ft.3  of  air. 

Thus  each  1000  ft.3  of  oxygen  demands  a  minimum 
energy  expenditure  of — 

2^49  H.P.H.  =  2-61  H.P.H. 

0'2I 

As  will  be  seen  below,  a  considerably  greater  energy 
expenditure  is  demanded  in  practice.  In  order  to  effect 
the  condensation  of  air  by  means  of  a  bath  of  liquid  air 
boiling  under  atmospheric  pressure,  a  certain  compression 
is  required,  increasing  as  the  nitrogen  boils  off  from  the 
liquid  bath.  In  practice,  a  compression  of  from  3  to  5 
atmospheres  is  used.  As  regards  losses  in  the  heat-inter- 
changers,  we  may  take  the  efficiency  as  being  of  the  order 
of  95%-* 

We  will  now  pass  to  the  consideration  of  the  different 
systems  for  the  separation. 

MANUFACTURE  OF  OXYGEN  AND  NITROGEN 
Linde  System 

The  principle  of  rectification  was  first  applied  technically 
by  Linde  in  1895  (cf.  B.P.  12528/95),  but  the  main  features 
of  the  Linde  plants,  except  the  most  recent,  are  to  be  found 
in  B.P.s  14111/02  and  11221/03.  Since  the  production  of  pure 
nitrogen  together  with  impure  oxygen  requires  a  somewhat 
different  procedure  from  that  of  the  production  of  pure  oxygen 
together  with  impure  nitrogen,  slightly  different  types  of 

*  According  to  Claude,  one  litre  of  liquid  air  is  evaporated  in  the 
fractionation  of  the  air  corresponding  to  30  litres  of  liquid  air. 
A.  6 


82  INDUSTRIAL  GASES 

apparatus  are  used  for  the  two  purposes.  It  usually  happens, 
unfortunately,  that  there  are  not  adequate  demands  for  both 
oxygen  and  nitrogen  in  large  quantities  in  a  given  locality. 

Oxygen  Plants. — The  operation  of  the  plant  consists  of 
two  stages  :  (i)  cooling  down  the  air  and  producing  a 
sufficient  quantity  of  liquid  air  ;  (2)  fractionation  of  such 
liquid  air  with  sufficient  replacement  to  compensate  for 
thermal  leakages.  Air,  at  a  pressure  of  about  135  atms., 
passes  through  three  small  tubes  in  the  heat-inter  changer, 
consisting  of  the  copper  tube  C  (Fig.  n,  cf.  Engineering,  99, 
(1915),  155)  containing  the  smaller  copper  tubes,  in  counter- 
current  to  the  outgoing  gases.  After  traversing  the  coils 
di,  expansion  occurs  at  the  valve  G,  the  cooled  expanded 
gases  being  discharged  through  a  rose-ended  pipe,  d%.  As 
cumulative  cooling  takes  place,  liquefaction  ensues  and 
liquid  flows  down  the  column  A,  and  collects  in  the  chamber 
B.  Presently  liquefaction  occurs  in  the  coils  di  themselves 
and  the  pressure  of  the  incoming  compressed  air  is  reduced 
by  gradually  opening  G.  A  steady  stream  of  liquid  now 
falls  down  the  column  A,  being  derived,  for  the  greater  part, 
at  the  expense  of  the  partial  evaporation  of  the  accumulation 
in  the  chamber  B.  This  stream  of  liquid  meets  the  counter- 
current  of  gas  from  the  chamber  B,  and  mutual  fractionation 
results. 

As  the  liquid  progresses  down  the  column  the  tempera- 
ture gradually  rises  and  the  oxygen  content  continually 
increases  ;  consequently,  the  liquid  reaching  the  bottom  is 
practically  pure  oxygen,  while  the  ascending  gas  loses  oxygen 
until  its  oxygen  content  is  equal  to  that  in  equilibrium  with 
liquid  air  containing  21  %  oxygen,  viz.  7  %.  This  means 
that  some  28  %  of  the  total  oxygen  goes  off  with  the  nitrogen. 
When  a  steady  state  is  established  the  working  pressure  is 
about  50-60  atmospheres,  and  the  gases  leave  at  a  pressure 
of  about  5  lbs./in.2,  sufficient  to  overcome  the  resistance 
of  the  heat-interchangers. 

The  oxygen  leaves  the  apparatus  at  el.  As  in  all  similar 
apparatus,  the  preliminary  purification  of  the  air  from 
water  and  carbon  dioxide  is  very  important.  The  water 


AIR  83 

is  often  removed  by  p  re-cooling  the  air  with  an  ammonia 
plant,  using  duplicate  coolers  which  are  changed  over  three 
or  more  times  weekly ;  this  procedure  has  the  further 
advantage  of  increasing  the  efficiency,  the  separator 

rr-o 


FIG.  ii. — Linde  Oxygen  Plant  (Engineering). 

itself  runs  for  about  a  week  before  blockage  occurs ;  it  is 
usually  advisable  to  duplicate  the  separator  in  such  plants. 
Instead  of  producing  the  liquid  air  in  the  separator  itself, 
the  latter  may  be  fed  with  liquid  air  produced  in  an 
independent  plant. 


84 


INDUSTRIAL   GASES 


The  lyinde  patent  rights  for  the  United  Kingdom  were 
acquired  in  1906  by  the  British  Oxygen  Co.,  which  now  pro- 
duces most  of  the  oxygen  used  in  this  country  by  the  L,inde 
process.  According  to  Murray,  a  usual  size  of  plant  is  one 
absorbing  100  B.H.P.  and  producing  about  1650  ft.3  of 
oxygen  per  hour  (i.e.  60  B.H.P.H.  per  1000  ft.3  oxygen, 
or,  say,  53  K.W.H.  if  the  efficiency  of  the  motor  ==  85  %). 

The  following  table  gives  particulars  of  various  sizes  of 
Ivinde  plants  as  regards  power  expenditure,  etc  : — 


TABLE  1 8. 
LINDE  OXYGEN  PLANTS. 


Oxygen  production, 

ft.8  per  hour 

35 

70 

175 

350 

700 

i,75° 

3.5°° 

7,000 

I7»50<> 

35,ooo 

Power  (measured  on 

the  switchboard), 

K.W  

4'5 

7'5 

15 

26 

41 

75 

138 

260 

600 

1,120 

K.W.H./iooo  ft.8  of 

oxygen 

129 

107 

86 

74 

59 

43 

39 

37 

34 

32 

Cooling  water,  gal- 

lons per  hour 

55 

no 

220 

350 

530 

880 

1,540 

2,860 

6,400 

11,900 

Nitrogen  Plants. — The  I^inde  nitrogen  rectifier  is  very 
similar  in  general  arrangement  to  that  just  described  for 
oxygen  production,  and  is  shown  in  Fig.  12  (cf.  Engineering, 
99,  (1913),  156).  Two  gas  supplies  are  used  :  (i)  air  at  an 
initial  pressure  of  about  135  atms.  to  produce  and  maintain 
the  charge  of  liquid  air  ;  (2)  air  at  a  pressure  of  about 
60  lbs./in.2.  Pre-cooling  may  be  used  with  advantage,  and 
direct  addition  of  liquid  air  may  be  substituted  for  (i). 
The  liquid  air  resulting  from  (i)  is  fed  to  the  top  of  the 
column  while  the  low  pressure  air  is  led  through  coils  in  B, 
is  there  liquefied  and  then  released  through  the  valve  G  to 
the  central  portion  of  the  column.  In  the  column,  as  before, 
rectification  takes  place  down  to  an  oxygen  content  of  7  % , 
in  which  state  of  purity  the  nitrogen  leaves  the  separator 
through  the  pipe  C.  The  high  pressure  compressor  is  then  fed 
with  part  of  this  effluent,  with  the  result  that  the  liquid  at  the 


AIR  85 

top  of  the  column  contains  only  7  %  oxygen  and'  can  conse- 
quently reduce  the  oxygen  content  of  the  ascending  gas  to 
about  2  % .  In  this  way  a  cumulative  rectification  is  produced 
and  eventually  the  gas  issuing  at  C  is  practically  pure  nitrogen. 


FIG.  12. — Linde  Nitrogen  Plant. 

The  purity  of  the  oxygen  fraction  is  often  not  very  high. 
The  power  expenditure  is  about  14*2  H.P.H.  per  1000  ft.3 
of  nitrogen,  according  to  Murray,  equivalent  to  12-4  K.W.H. 
per  1000  ft.3  if  efficiency  of  motor  =  85  %.  One  of  the  largest 
plants  in  operation  before  the  war  was  that  at  the  Cyanamide 


86 


INDUSTRIAL   GASES 


Works  at  Odda,  capable  of  producing  13,000  ft.3  (0-43  ton) 
of  nitrogen  per  hour. 

The  following  table  gives  particulars  of  various  sizes  of 
nitrogen  plants  : — 


TABLE    19. 
LINDE  NITROGEN  PLANTS. 


Nitrogen     pro- 

duction,  ft  3 

per  hr. 

210 

425 

1,  060 

2,100 

4.250 

10,600 

21,000 

42,500 

106,000 

210,000 

Power      (mea- 

sured on  the 

switchboard). 

! 

K.W. 

4'5 

9 

22 

39 

60 

112 

205 

373 

820 

1,490 

K.W.H./iooo 

ft.8  nitrogen 

21-4 

21'2 

20'7 

18-6 

14-1 

io'6 

9'8 

8-8 

r  75 

7-1 

Cooling   water. 

Gallons     per 

hr  

165 

198 

330 

57° 

880 

1,650 

2,820 

4,400 

8,360 

16,500 

New  Linde  System. — According  to  later  L,inde  patents 
(D.R.P.  203814/06)  rectification  is  pushed  further  by  effecting 
a  preliminary  fractionation  under  about  4  atms.  pressure, 
and  thus  obtaining  a  supply  of  liquid  approximating  to 
pure  nitrogen  for  the  final  fractionation.  Thus,  column  b 
(Fig.  13)  is  fed  with  air  at  about  4  atms.  pressure  at  a.  The 
oxygen-rich  liquid  collecting  at  the  bottom  of  this  column 
is  taken  to  the  vessel  e  at  the  top,  the  pressure  being  broken 
down  to  atmospheric  at  the  valve  g.  As  the  gas  inside  the 
coil  c  is  under  a  pressure  of  4  atms.,  complete  liquefaction 
will  ensue,  the  first  condensate  being  thus  of  21  %  oxygen 
content.  Since  the  gas  in  equilibrium  with  liquid  of  this 
composition  at  4  atms.  contains  about  10  %  oxygen,  the 
oxygen  content  of  the  liquid  condensing  in  c  will  fall  off 
and  eventually  almost  pure  nitrogen  will  result.  A  portion 
of  the  crude  nitrogen  from  the  top  of  b  is  led  to  the  spiral 
d  immersed  in  the  tank  h  at  the  bottom  of  the  low  pressure 
column  k  and  containing  almost  pure  oxygen.  Here 
liquefaction  occurs,  the  liquid  being  led  via  the  valve  *, 
where  the  pressure  is  released,  to  the  top  of  the  column  k, 
in  which  further  rectification  results.  The  oxygen-rich 


AIR 


87 


liquid  from  /  is  vaporized  in  e,  the  vapours  being  led  to  the 
lower  part  of  k.  Pure  nitrogen  and  oxygen  leave  the 
apparatus  at  n  and  m  respectively.  According  to  Martin, 
when  worked  specially  for  oxygen  some  85-90  %  of  the 
oxygen  is  obtained  as  such.  The  energy  consumption  is 
about  37  K.W.H.  per  1000  ft.3  of  oxygen.  Similarly  it  is 


FIG.  13. — New  Linde  System. 

possible  to  produce  nitrogen  of  about  997  %  purity  with 
an  energy  expenditure  of  about  11-3  K.W.H.  per  1000  ft.3 
of  nitrogen. 

Claude  System 

In    the    Claude    system    the    problem    of    feeding    the 
fractionating  column  with  a  liquid  poorer  in  oxygen   than 


88  INDUSTRIAL   GASES 

that  corresponding  to  ordinary  air  is  attacked  by  effecting 
a  preliminary  rectification,  employing  what  the  inventor 
terms  the  "  backward  return,"  equivalent  to  a  reflux  con- 
denser arrangement  (B.P.s  16298/03,  26435/05,  17216/09, 
etc.).  Thus,  air  at  a  pressure  of  about  40  atms.  enters  the 
apparatus  through  the  heat-interchangers  B  and  K1  (Fig.  14), 
undergoing  partial  liquefaction  in  Iy  by  heat-interchange 
with  the  cold  gases  leaving  at  the  top  of  M.  The  residual 
air  enters  the  rectification  apparatus  at  A  and  undergoes 
partial  liquefaction  in  passing  up  the  tubes  B,  cooled  ex- 
ternally by  liquid  air.  Further  liquefaction  occurs  in  the 
downward  path  with  the  production  of  a  nitrogen-rich 
fraction  in  A1  while  an  oxygen-rich  fraction  collects  in  A. 
These  two  fractions  are  fed  into  the  column  at  different 
levels,  as  in  other  systems. 

The  low  temperature  of  the  nitrogen  issuing  at  G  is 
utilized  for  a  preliminary  liquefaction  of  the  incoming  air 
at  I,,  as  explained  above,  while  thermal  leakage  into  the 
system  is  made  good  by  expansion,  with  performance  of 
external  work,  of  part  of  the  incoming  air  in  the  cylinder  O. 
When  admitted  to  the  tubes  B,  the  air  is  at  a  pressure  of 
about  5  atms.,  suffering  release  to  atmospheric  pressure  at  R 
and  R1  respectively.  Liquid  air  from  an  independent  source 
may  be  used  to  charge  the  apparatus,  or,  in  the  latest  types, 
the  necessary  charge  is  produced  by  the  expansion  device. 
The  pressure  at  X  ranges  from  about  40  atms.,  when  filling 
up  with  liquid  air,  to  a  lower  value  in  normal  running, 
varying  according  to  the  size  of  the  installation,  and  being 
as  low  as  18  atms.  for  large  plants.  The  nitrogen  obtained 
in  this  way  contains  in  practice  about  3  %  oxygen.  Nitrogen 
of  a  purity  of  99*5%  upwards  can,  however,  be  obtained 
(B.P.  7175/10)  by  preventing  the  liquid  dropping  into  the 
chamber  surrounding  the  tubes  B  from  mixing  immediately 
with  the  main  liquid  therein,  by  disposing  a  separate  tray 
round  the  upper  part  of  the  tubes  B.  Thus,  the  entering 
liquid,  at  a  lower  temperature  than  the  main  bulk  of  liquid 
because  of  lower  oxygen  content,  is  utilized  to  lower  the 
oxygen  content  of  the  gaseous  nitrogen.  There  are  at 


AIR 


89 


present  a  large  number  of  plants  in  operation,  the  most 
usual  sizes  being  175-700  ft.3  oxygen  per  hour. 


FIG.  14. — Claude  Fractionation  System. 

The    following   table    indicates    the    sizes    and   power 
requirements     of     Claude     plants    (cf.    Mewes,    loc.    cit., 

P-  77)  :— 


90  INDUSTRIAL   GASES 


TABLE  20. 
CLAUDE  OXYGEN  PLANTS. 


Oxygen  production,  ft.3  per  hour 

i,75o 

3,500 

Power  (measured  on  the  switchboard). 

K.W  

.  . 

56 

78 

K.W.H./iooo  ft.3  of  oxygen 

32 

22 

Pictet  System 

The  Pictet  system  for  oxygen  and  nitrogen  (B.P.s 
27463/10  and  9357/13 ;  cf.  Maxted,  J.  Soc.  Chem.  Ind., 
(1917),  778),  which  is  claimed  to  be  very  economical  of 
power  by  reason  of  employing  only  an  approximation  to  the 
minimum  theoretical  pressure  for  liquefaction,  operates  as 
follows.  Cooled  air,  at  practically  atmospheric  pressure, 
is  led  into  the  middle  of  a  fractionating  column  (Fig.  15). 
A  series  of  coils  is  arranged,  in  a  number  of  separate  systems, 
on  the  plates  of  the  column  and  is  supplied  with  compressed 
gas  drawn  by  the  pump  /  from  the  top  of  the  column  at 
which  point  the  pressure  is  released  from  all  the  coils.  Some 
liquid  air  being  first  placed  in  the  column,  liquefaction 
occurs  in  the  coils  and  presently  the  gas  leaving  at  the  top 
will  contain  7  %  oxygen.  On  liquefaction  this  will  exert  a 
further  refining  action  on  the  ascending  air  and  pure  nitrogen 
will  issue  at  the  top  of  the  column.  The  liquid  collecting 
at  the  bottom  of  the  column  is  practically  pure  oxygen. 

In  order  to  avoid  the  employment  of  more  pressure  than 
is  necessary  for  the  liquefaction  and,  further,  to  ensure 
uniform  fractionation  along  the  length  of  the  column,  the 
coils,  as  mentioned  above,  are  divided  into  sections ;  the 
air  is  admitted  at  the  bottom  at  a  pressure  of  about  5  atms., 
while  the  uppermost  section  is  fed  with  air  only  slightly 
above  atmospheric  pressure  in  accordance  with  the  tempera- 
ture gradient  in  the  fractionation  column,  the  pressure  in 
each  case  being  just  sufficient  to  produce  liquefaction  of 
the  nitrogen.  The  usual  heat-interchangers  are  employed 
and  the  losses  are  made  good  by  the  liquefaction  of  part  of  the 


AIR  91 

issuing  nitrogen  by  means  of  expansion  with  the  production 
of  external  work. 

A  plant  on  this  system,  with  a  capacity  of  14,000  ft.3  of 


FIG.  15. — Pictet  System. 

nitrogen  and  3500  ft.3  of  oxygen  per  hour,  has  been  installed 
at  the  works  of  Gas  Develop ments,  L/td.,  Walsall. 

Among  other  systems  of  importance  may  be  cited  the 
Hildebrandt  system,  which,  in  general  principle,  does  not 


92  INDUSTRIAL  GASES 

differ  greatly  from  the  l/inde  system.  A  Hildebrandt  plant 
producing  350  ft.3  of  oxygen  per  hour  absorbs  about  27  K.W. 
in  power. 

Separation  of  the  Rare  Gases. — In  the  ordinary  opera- 
tion of  liquid  air  fractionation  plants,  the  rare  gases  divide 
themselves  between  the  oxygen  and  nitrogen  according  to 
their  boiling  points.  Thus,  the  oxygen  fraction  contains  a 
higher  concentration  of  argon  than  the  nitrogen  fraction, 
while  the  nitrogen  fraction  is  richer  in  neon  and  helium. 
By  means  of  suitable  additional  fractionation  arrangements 
it  is  possible  to  separate  the  rare  gases  individually  hi  a 
state  of  much  greater  concentration,  and  some  account  of 
such  methods  will  be  found  under  the  rare  gases. 


REFERENCES  TO   SECTION  I 

Claude,  "  Liquid  Air,  Oxygen,  Nitrogen  "  (Cottrell).     London,  1913. 

Kausch,  "  Die  Herstellung,  Verwendung  und  Aufbewahrung  von 
fliissiger  Luft."  Weimar,  Fourth  Edition,  1913. 

Travers,  "The  Experimental  Study  of  Gases."     London,  1901. 

Anon.,  "  The  Use  of  Liquid  Air  in  Industry,"  Engineering,  99,  (1915),  155. 

Linde,  "Separation  of  the  Constituents  of  Mixtures  of  Gases  by  Lique- 
faction," /.  Soc.  Chem.  Ind.,  (1911),  744. 

Garner,  "  On  the  Theoretical  Efficiency  of  the  Linde  Process  of  Liquefying 
Air,"  /.  Franklin  Inst.,  177;  (1914),  305. 

Mewes,  "Angaben  uber  Kraftverbrauch  und  Leistung  von  Luftverfliissig- 
ungs-  und  Sauerstoff  Anlagen,"  Z.fur  Sauerstoff  und  Stickstoff  Industrie,  5, 
(1913),  317;  "Uber  die  Wirtschaftlichkeit  moderner Luftverflussigungs- und 
Gastrennungs- Anlagen,"  Ibid.,  5,  (1913),  175;  "  Sauerstofferzeugungs- 
Anlage  System  Hildebrandt,"  Ibid.,  2,  (1910),  134,  160,  204,  281  ;  4, 

(IQI2),  108. 


SECTION  II.— OXYGEN 

Properties  of  Oxygen. — Oxygen  is  a  colourless,  odourless 
and  tasteless  gas,  of  which  the  chief  physical  properties 
will  be  found  in  Table  12,  pp.  53-55. 

According  to  Holborn  and  Austin  (loc.  cit.,  p.  58) 
the  mean  specific  heat  varies  with  temperature  as 
follows : — 


Temperature  °  C. 

CP 

20—440 
20—630 

0-2240 
0-2300 

Its  solubility  in  water  is  expressed  by  the  following  table  : — 


Temperature  °C. 

o 

IO 

15 

20 

40 

C.c.  of  gas  (measured  at  N.T.P.) 

dissolved    by  I    c.c.  of   water 
under  a  pressure  of  i  atm.,  ex- 

0-049 

0-038 

0-034 

0-031 

0-023 

clusive  of  water  vapour. 

Liquid  oxygen  is  extremely  mobile  with  a  faint  blue 
colour,  and  the  density  of  the  vapour  agrees  with  the  formula 
O2  at  —  182°  C.  The  liquid  is  a  non-conductor  of  electricity, 
but  is  strongly  magnetic.  Its  refractive  index  (f*D)  is  1*2236 
and  its  specific  heat  0-347.  It  is  not  easy  to  obtain  pure 
liquid  oxygen  by  the  fractionation  of  liquid  air,  as  the  argon 
tends  to  accumulate  in  the  oxygen  fraction. 

Oxygen,  being  the  active  constituent  of  air  as  regards 
combustion,  supports  combustion  with  great  vigour,  thus, 
iron  wire  will  burn  freely  in  oxygen  when  once  started. 
Oxygen  is  readily  converted  into  ozone  by  the  action  of  the 
silent  discharge.  Molten  silver  absorbs  some  ten  times  its 
volume  of  oxygen,  the  gas  being  mostly  disengaged  on 
solidification. 


94  INDUSTRIAL  GASES 

MANUFACTURE  OF  OXYGEN 

General. — The  manufacture  of  oxygen  has  attracted  the 
attention  of  many  inventors  and  various  methods  have  been 
suggested.  One  of  the  earliest  patents  is  that  of  White 
(B.P.  12536/49),  relating  to  the  use  of  nitre.  In  the  early 
days  of  the  limelight  lantern  the  oxygen  was  mainly  produced 
by  the  classical  method  of  heating  a  mixture  of  potassium 
chlorate  and  manganese  dioxide,  while  the  use  of  manganese 
dioxide,  either  alone  or  with  sulphuric  acid,  was  adopted  to 
some  extent.  In  the  production  of  sulphuric  anhydride  by 
the  contact  process  a  mixture  of  sulphur  dioxide  and  oxygen 
was  formerly  prepared  by  the  decomposition  of  sulphuric 
acid  by  dropping  on  a  red-hot  surface  (Squire,  B.P.  3278/75). 
The  only  processes  which  have  been  worked  on  a  really  large 
scale  are  the  liquid  air  process  and  the  baryta  process, 
No  real  success  has  attended  work  directed  to  the  separation 
of  oxygen  from  the  atmosphere  by  physical  means,  except, 
of  course,  by  fractionation  of  liquid  air. 

Although  at  present  commercial  use  is  only  made  of 
oxygen  specifically  prepared,  it  is  probable  that  with  the 
advent  of  various  nitrogen  fixation  processes,  e.g.  the  Haber, 
Cyanamide,  Bucher  and  other  processes,  the  resulting 
by-product  oxygen  will  effect  a  great  cheapening  of  oxygen, 
not  necessarily  of  a  high  degree  of  purity,  for  many  purposes 
at  present  out  of  the  question  on  account  of  the  cost  of 
oxygen. 

(1)  Manufacture  by  the  Fractionation  of   Liquid 
Air. — For  a  description  of  this  method,  see  Section  I. 

(2)  By  Electrolysis. — Oxygen  is  liberated,  together  with 
hydrogen,  in  the  electrolysis  of  water.     A  full  description 
of  this  subject  will  be  given  under  electrolytic    hydrogen, 
Section  VI.,  and  all  quantitative  data  can  be  taken  from  this 
description,  the  yield  of  oxygen  being  approximately  half 
that  of  the  hydrogen. 

On  account  of  the  (past)  difficulty  of  its  disposal,  the 
hydrogen  produced  simultaneously  with  the  oxygen  has 
often  been  blown  to  waste  or  used  for  heating  purposes. 


OXYGEN  95 

The  hydrogen,  in  conjunction  with  the  oxygen,  ma*y,  how- 
ever, be  used  profitably  for  welding.  If  freed  from  traces 
of  intermixed  hydrogen  (which  may  amount  to  about  3  %) 
by  passage  over  a  heated  catalyst,  e.g.  palladized  pumice, 
the  oxygen  is  obtained  in  an  extremely  pure  state. 

On  account  of  its  very  high  purity  electrolytic  oxygen 
is  eminently  suitable  for.,  metal  cutting  operations  (cf. 
applications  of  oxygen) .  Electrolytic  oxygen  is  manufactured 
in  this  country  by  the  British  Oxygen  Co.,  L,td.,  at  Wolver- 
hampton,  using  the  Schuckert  cell. 

Many  attempts  have  been  made  by  various  inventors 
to  produce  oxygen  without  the  simultaneous  production 
of  hydrogen  ;  such  efforts,  however,  do  not  appear  to  have 
met  with  any  technical  success.  Thus,  Coehn  (cf.  D.R.P. 
75930/93)  proposes  the  use  of  (a)  cathodes  which  absorb 
hydrogen  and  are  subsequently  used  as  elements  of  a  gas 
cell ;  cf.  also  Brianchon,  F.P.  439737/12,  who  uses  a  gas  cell 
of  hydrogen  and  air  to  generate  current  for  the  decomposition 
of  water  ;  (b)  the  use  of  depolarizing  copper  oxide  cathodes. 
The  use  of  depolarizing  liquids  and  of  electrolytes  such  as 
copper  sulphate  solution,  employing  insoluble  anodes  and 
effecting  the  deposition  of  copper,  have  been  similarly  proposed. 

It  is  interesting  to  note  that  the  minimum  percentage 
of  hydrogen  required  to  produce  an  explosive  mixture  with 
oxygen  is  5-5  %,  the  influence  of  increased  pressure  on  the 
limiting  percentage  being  very  small  (cf.  p.  40). 

(3)  By  Alternate  Formation  and  Decomposition  of 
Higher  Oxides,  etc. — Prior  to  the  introduction  of  the  liquid 
air  method  about  1895,  the  only  processes  (other  than 
electrolytic)  which  had  been  used  for  the  production  of 
oxygen  on  anything  like  a  large  scale  come  under  this  cate- 
gory. The  patents  relating  to  the  subject  are  too  numerous 
to  be  given  in  full,  but  allusion  will  be  made  to  the  more 
important. 

As  early  as  1864  (B.P.s  2934/64  and  3171/66),  Mallet 
suggested  the  use  of  Cu2OCl2,  formed  by  exposing  cuprous 
chloride  to  moist  air ;  on  heating  to  dull  redness  oxygen  is 
evolved.  The  alternate  formation  and  decomposition  of 


96  INDUSTRIAL  GASES 

alkali  manganates  was  put  forward  by  Tessie  du  Motay  and 
Marechal  (B.P.  85/66).  By  heating  manganese  dioxide 
mixed  with  caustic  soda  to  dull  redness  in  a  current  of  air 
sodium  manganate  was  formed,  which  on  the  passage  of 
steam  at  a  bright  red  heat  gave  oxygen,  the  manganate 
reverting  to  Mn2O3  and  caustic  soda.  Several  works  were 
actually  erected  in  Europe  and  New  York,  but  the  life  of  the 
reactant  mass  was  found  to  be  rather  short,  largely  on  account 
of  segregation.  A  number  of  improvements  were  patented, 
e.g.  patents  having  as  object  the  prevention  of  segregation, 
while  Parkinson  (B.P.  14925/90)  employed  a  vacuum  instead 
of  steam,  the  air  being  pumped  in  under  pressure  and  the 
temperature  maintained  nearly  constant.  None  of  these 
processes,  however,  met  with  any  special  success. 

To  take  another  direction  of  investigation,  the  use  of 
alkaline  earth  plumbates  was  suggested  by  Kastner  in  B.P. 
1 1899/89.  Calcium  plumbate  is  formed  on  calcining  a  mixture 
of  calcium  carbonate  and  oxide  of  lead  in  air  and  may  be 
decomposed,  yielding  oxygen,  in  a  variety  of  ways,  e.g.  by 
treatment  with  sodium  carbonate  solution  and  subsequent 
heating  of  the  resulting  CaCO3  -fPbO2  precipitate  ;  by  carbon 
dioxide  in  suspension  in  water  or  by  the  action  of  carbon 
dioxide  without  removal  from  the  furnace.  None  of  these 
processes,  however,  is  very  practical.  According  to  a 
modified  form  of  the  process  a  combination  of  alkali  manga- 
nate and  metaplumbate  was  used  under  the  name  of  "  Plumb- 
oxan  "  (B.P.  12307/11),  the  mass  being  treated  alternately 
with  air  and  steam  at  a  temperature  of  400-500°  C. 

A  greater  measure  of  success  has  attended  the  use  of 
barium  peroxide,  the  dissociation  pressure  of  which  is  greater 
than  that  of  Ca2PbO4.  First  suggested  by  Boussingault  in 
1851,  it  was  developed  by  Messrs.  Brin's  Oxygen  Co.  about 
1886  (cf.  B.P.  1416/80).  It  was  originally  operated  using  a 
considerable  temperature  variation,  but  by  means  of  pressure 
variation  the  time  of  oxygen  evolution  was  shortened  from 
about  4  hours  to  about  15  minutes,  a  considerably  lower 
temperature  being  sufficient.  Further,  by  means  of  a  suitable 
arrangement  of  valves  (Brin's  Oxygen  Co.  and  Murray, 


OXYGEN 


97 


B.P.s  4955/89,  4292/91  and  14918/93),  the  operations  were 
rendered  automatic,  four  cycles  per  hour  being  adopted,  this 
procedure  tending  to  greater  regularity  of  working  and 
minimizing  wear  and  tear  on  the  retorts.  According  to 
B.P.  17298/91  the  baryta  is  disposed  on  pumice. 

The  baryta  used  is  obtained  in  a  hard,  porous  state  by 
ignition  of  the  nitrate  ;  it  is  important  to  purify  the  air 
from  carbon  dioxide  and  from  most  of  its  moisture  (by  lime 
and  then  caustic  soda)  before  pumping  into  the  retorts, 
since  both  barium  carbonate  and  barium  hydroxide  are 
stable  at  high  temperatures.  The  presence  of  a  little  water 
vapour  is  necessary  since  it  acts  as  a  catalyst.  The  vertical 
steel  retorts,  containing  lumps  of  about  walnut  size,  are 
heated  to  about  600°  C.  Air  at  a  pressure  of  about  10  lbs./in.2 
passes  through  the  purifiers  and  then  to  the  retorts,  the 
residual  nitrogen  escaping  through  a  snifting  valve.  After 
about  7  minutes,  connection  is  made  to  a  vacuum  of  about 
26  ins.  of  mercury,  the  first  portion  of  the  oxygen  being 
rejected.  The  rate  of  production  may  be  expressed  as — 

(1)  About  0*5  ft.3  oxygen/lb.  baryta/hour. 

(2)  About  25  ft.3  oxygen/ft.3  retort  capacity /hour. 
(Cf.  Murray,  Proc.  Inst.  Mech.  Engineers,  (1890),  131.) 

The  effect  of  the  pressure  variation  can  be  readily  seen 
from  the  following  dissociation  pressures  (Hildebrand,  /. 
Amer.  Chem.  Soc.,  34,  (1912),  246),  for  barium  peroxide  in  the 
presence  of  a  little  water  : — 


Temperature  °C. 

618 

655 

697 

737 

794 

835 

853 

868 

Oxygen     pressure    in 

cms.  of  mercury     .  . 

11-3 

26-8 

6.5-4 

141 

378 

718 

937 

1166 

Water  vapour  pressure 

in  cms.  of  mercury 

7'3 

13'  7 

26-3 

47 

98 

159 

195 

231 

Until  recent  years  the  baryta  process  was  used  extensively 
in  the  works  of  the  Brin's  Oxygen  Co.  (now  the  British 
Oxygen  Co.),  e.g.  in  1907  three  works  were  producing  30,000 
ft.3  of  oxygen  per  day  ;  it  has  now  been  superseded  by  the 
liquid  air  process  not  only  on  account  of  its  lower  cost  but 
also  because  of  the  greater  purity  of  the  liquid  air  oxygen 
A.  7 


98  INDUSTRIAL   GASES 

(about  98  %  as  compared  with  about  95  %  by  the  baryta 
process) . 

Other  processes  on  similar  lines  have  been  proposed,  e.g. 
the  use  of  hsemoglobin  (Sinding-L,arsen  and  Storm,  B.P.s 
8211/10  and  12728/10),  the  use  of  nitrosulphonic  acid 
(Bergfeld,  B.P.  21211/13),  etc.,  cf.  also  Teissier  &  Chaillaux, 
see  p.  206. 

(4)  By  Auto-combustion  Methods. — The  development 
of  such  methods  of  preparing  oxygen  (cf .  also  the  production 
of  hydrogen  from  "  Hydrogenite,"  Section  VII.,  p.  227)  is 
mainly  due  to  the  French  chemist,  Jaubert,  who  in  a  series 
of  patents  (B.P.s  24330/05,  12246/06,  and  12262/06) 
proposes  the  employment  of  a  mixture  of  perchlorates  or 
nitrates  in  excess,  with  a  combustible  material,  an  inert 
diluent  being  added,  if  desired.  Special  apparatus  is  described 
in  B.P.s  12834/06;  1256/07,  17252/07,  and  22034/09. 

Briefly,  the  apparatus  consists  of  a  steel  cylinder  in  which 
is  suspended  a  perforated  cylinder  containing  the  mixture, 
known  as  "  Oxygenite."  The  mixture  is  ignited  and  the 
lid  rapidly  closed  when  the  reaction  prop  agates  itself  through- 
out the  mass.  Oxygen  collects  in  the  annular  space  sur- 
rounding the  inner  cylinder  at  a  pressure  of  about  12  atms. 
The  yield  per  Ib.  of  "  Oxygenite  "  is  about  4  ft.3  and  the  cost 
about  £5/1000  ft.3.  It  is  at  once  obvious  that  the  process 
is  very  expensive  in  comparison  with  the  liquef action  process, 
but  there  are  advantages  for  some  special  cases  in  the  avoid- 
ance of  transport  of  cylinders,  availability  for  mine  rescue 
work,  etc. 

Some  slight  modifications  are  due  to  Harger  (B.P.s 
16693/10  and  17628/10),  the  mixture  of  a  chlorate  and  lamp- 
black, with  addition  of  a  catalyst  such  as  manganese  dioxide 
and  also  of  caustic  soda  if  carbon  dioxide  be  produced  in  the 
reaction,  being  used  in  the  form  of  pencils;  a  continuous 
feed  of  the  pencils  may  be  arranged.  The  hot  oxygen  is 
led  back  through  the  unused  material  and  through  a  purifier. 

Other  patents  relate  to  alternative  mixtures  which  may 
be  used. 

(5)  By  the  Action  of  Water  on  Peroxides  and  the 


OXYGEN  99 

Like. — Examination  of  the  patent  literature  reveals  a  large 
number  of  patents  dealing  with  this  method  of  making 
oxygen.  To  take  a  typical  example,  sodium  peroxide  reacts 
energetically  with  water  according  to  the  following  equation  :— 

2  Na2O2  +  2  H2O  =  4  NaOH  +  O2 
Thus,   Jaubert,   in  B.P.  11466/01,  proposes  the  use  of 
mixtures  of  alkali  or  alkaline  earth  peroxides  with  alkali 
or  alkaline  earth  hypochlorites  in  the  form  of  pastilles,  which 
generate  oxygen  on  treatment  with  water. 

CaOCl2  -f  Na202  +H2O  =Ca(OH)2  +2NaCl  +O2 

A  later  patent  (B.P.  21122/03)  deals  with  the  use  of 
mixtures  such  as  a  solution  of  bleaching  powder  with  the 
addition  of  catalysts  as  copper  sulphate  and  iron  sulphate, 
while  Artigue,  in  B.P.  14848/04,  protects  apparatus  for  carry- 
ing this  process  into  operation.  Hanman,  in  B.P.  9783/03, 
describes  the  mixture  known  as  "Oxy lithe/'  *  while  the  use 
of  fused  sodium  peroxide  is  suggested  by  Foersterling  and 
Philipp  in  B.P.  3820/05.  Among  the  various  patents  for 
apparatus  may  be  mentioned  that  of  Ransford  (B.P.  9785/02). 
Other  patents,  e.g.  Byk  (B.P.  7495/09),  describe  the  use  of 
perborates  with  the  addition  of  stabilizers  and  catalysts. 

Preparations  on  the  market  such  as  "  Oxy lithe  "  are 
useful  for  laboratory  purposes. 

"  Oxy  lithe  "  may  be  used  in  a  Kipp's  apparatus,  one  Ib. 
giving  about  3  ft.3  of  oxygen  while  "  Bpurite  "  (=  bleaching 
powder  +  iron  sulphate  +  copper  sulphate)  is  suitable  for 
use  on  a  larger  scale,  but  in  either  case  the  oxygen  is  very 
expensive. 

Experiments  have  been  made  with  sodium  peroxide 
preparations  for  revivifying  the  air  of  submarines,  oxygen 
being  liberated  by  the  moisture  of  the  breath  while  the 
resulting  caustic  soda  serves  to  remove  the  carbon  dioxide. 

(6)  By  Physical  Methods  (in  the  Gaseous  State).— 
In  view  of  the  fact  that  the  solubilities  of  oxygen  and  nitrogen 
in  water  at  15°  C.  are  0-034  an(i  0*0179  respectively  for 

*  Sodium  peroxide  .  .  98*32  per  cent. 
Oxide  of  iron  . .  . .  1*00  per  cent. 
Copper  sulphate  . .  o-68  per  cent. 


ioo  INDUSTRIAL  GASES 

i  atm.  pressure,  it  is  obvious  that  the  respective  volumes 
dissolved  on  shaking  water  with  air  are  in  the  ratio  0*034  X  z  : 
0-0179x4  =  1  :  2*1,  since  the  partial  pressures  of  oxygen 
and  nitrogen  are  0*1  and  0*4  respectively.  Consequently 
the  gas  evolved  on  reducing  the  pressure  or  raising  the 
temperature  is,  if  all  the  gas  be  driven  out,  of  the  composition 
N2  :  O2  =  2'i  :  i,  i.e.  32  %  oxygen,  as  against  the  original 
21  %.  Many  attempts  to  effect  an  economic  separation 
have  been  made  on  these  lines  ;  thus,  Mallet  (B.P.  2137/69) 
saturated  water  with  air  under  pressure  and  afterwards 
exposed  to  a  vacuum.  After  some  8  repetitions  the  gas 
evolved  was  97  %  oxygen.  Other  patents,  e.g.  Kubierschky 
(B.P.  17780/99),  Humphrey  (B.P.  14809/05),  Levy  (B.P. 
5931/09),  are  similar. 

Although  the  technical  prospects  of  manufacturing 
pure  oxygen  by  such  processes  are  small  there  would  appear 
to  be  some  possibility  of  making  oxygen-enriched  air  economi- 
cally, e.g.  by  waterfalls  in  conjunction  with  arc  processes, 
etc.  The  same  statement  might  be  made  with  reference  to 
sundry  patents  relating  to  separation  by  centrifugalization 
(Mazza,  13598/07)  ;  by  diffusion  (Runge,  B.P.  3420/14), 
or  by  transpiration  through  indiarubber,  etc.,  (Helouis,  B.P. 
2080/81  ;  Neave,  B.P.  6463/90  ;  de  Villepique,  Fournier 
and  Shenton,  B.P.  19044/96  ;  Bartelt,  B.P.  24428/06). 

None  of  these  processes  appears  to  have  been  applied 
technically,  the  liquid  air  process  being  apparently  the  only 
really  successful  case  of  the  application  of  physical  methods. 

The  lyinde-Frank-Caro  process  for  the  manufacture  of 
hydrogen  (cf .  p.  172)  may  be  so  operated  as  to  yield  oxygen 
and  nitrogen  as  by-products  in  connection  with  the  cooling 
of  the  water  gas  (the  oxygen  =  about  25  %  of  the  hydrogen 
produced). 

Compression  of  Oxygen. — For  a  discussion  of  the 
precautions  to  be  observed  in  connection  with  the  com- 
pression of  oxygen,  see  p.  34.  In  this  country  oxygen  is 
sold  under  a  pressure  of  120  atms.,  in  black-painted  cylinders, 
the  capacity  of  which  does  not  usually  exceed  ioo  ft.3.  It 
is  most  important  that  no  oil  or  grease  of  any  kind  should 


OXYGEN 


inr 


be  allowed  to  come  into  contact  with  the  compressed  gas,  as 
serious  explosions  may  thus  be  caused.  Steel  should  not  be 
used  in  the  construction  of  the  cylinder  valves  since  com- 
bustion of  steel  spindles  has  been  known  to  occur,  being 
started  by  heat  engendered  by  friction. 

Comparison  of  Costs  of  Production  and  Purity 
Attainable  by  Different  Processes 

It  is  difficult  to  give  more  than  a  very  approximate 
comparison  of  the  costs  of  the  different  processes  which  have 
been  described  in  connection  with  the  manufacture  of  oxygen, 
but  the  following  table  will  serve  to  give  some  idea  of  the 
advances  which  have  been  made  in  this  branch  of  technology. 
All  costs  are  on  a  pre-war  basis  : — 

TABLE  21. 
COST  OF  PRODUCTION  AND  PURITY  OF  OXYGEN  BY  DIFFERENT  PROCESSES. 


Method. 

Cost  per  1000  ft.3 

Purity. 

From  potassium  chlorate 

^8-10 

Liable  to  contain  traces 

of  chlorine. 

From  manganese  dioxide 

*^4-6 

— 

By  the  Tessie  du  Motay  process 

*^3~4 

— 

By   the   decomposition    of    sul- 

*^2-3 

— 

phuric  acid 

— 

Kassner  process  .  . 

*High 

— 

Brin  process 

*7S.  tO  I2S. 

About  95  %. 

By  solution  in  water,  et 

*£>? 

— 

Oxygenite  process 

— 

[Oxylithe.] 

L£IO1 

Epurite  process 

? 

— 

By  electrolysis     .  . 

t  — 

Almost  perfectly 
passed  over  a 

pure  if 
heated 

catalyst. 

From  liquid  air   .  . 

*3s.  6d. 

About  98  %. 

The  values  of  cost  marked  with  an  asterisk  are  taken 
from  Thorpe's  "Dictionary  of  Applied  Chemistry,"  1912, 
vol.  4,  40 ;  they  are  apparently  exclusive  of  overhead 
charges.  In  the  case  of  the  liquid  air  process  the  overhead 

f  It  is  difficult  to  give  any  cost  for  electrolytic  oxygen,  as  it  depends 
so  much  on  the  price  of  electric  energy  and  the  use  to  which  the  hydrogen 
is  put.  For  any  particular  case,  however,  reference  to  the  section  on 
electrolytic  hydrogen  will  supply  the  desired  information. 


102  INDUSTRIAL  GASES 

charges  may  be  taken  as  of  the  order  of  1/6  per  1000  ft.3 
of  oxygen. 

As  regards  purity,  it  is  important  to  note  that  in  the 
liquid  air  process  about  half  of  the  argon  initially  present 
in  the  air  (about  0-9  %)  goes  into  the  oxygen  fraction.  The 
percentage  of  argon  is  consequently  higher  in  the  oxygen 
than  in  the  nitrogen.  A  brief  consideration  of  the  respective 
boiling  points  of  the  three  gases,  viz.  nitrogen  — 196°  C., 
oxygen  —183°  C.,  argon  — 186°  C.,  will  indicate  the  reason 
for  this.  "  Liquid  air"  oxygen,  therefore,  usually  contains 
some  2-3  %  of  argon.  Electrolytic  oxygen,  on  the  other 
hand,  can  be  produced  in  an  almost  pure  state. 

For  the  influence  of  purity  on  the  technical  applications 
cf.  "Metal  cutting,"  p.  105. 

Oxygen  manufactured  by  the  liquid  air  process  contains 
small  quantities  of  organic  matter  which  are  liable  to  introduce 
errors  in  organic  combustions  and  similar  operations.  When 
one  bears  in  mind  the  presence  of  traces  of  methane  and  other 
hydrocarbons  in  the  atmosphere  (cf.  p.  59),  this  fact  is  not 
surprising  ;  such  impurities  would  tend  to  be  concentrated 
in  the  less  volatile  oxygen  fraction. 

Applications  of  Oxygen 

The  applications  of  oxygen  are  very  diverse  and  it  will 
be  well  to  discuss  them  under  a  number  of  headings  as  below. 
Some  150-200  million  ft.3  of  oxygen  were  manufactured 
in  Great  Britain  in  1913.  According  to  Dewar  (/.  Soc. 
Chem.  2nd.,  (1919),  23  R),  the  present  output  of  the  twelve 
oxygen  factories  is  about  i  million  ft.3/day. 

About  90  %  of  the  above  production  is  absorbed  by 
the  welding  and  metal  cutting  industries  in  roughly  equal 
proportions. 

(1)  Scientific  and  Laboratory  Uses. — Oxygen  is  used 
in  the  laboratory  for  effecting  organic  combustions,  working 
quartz  or  hard  glass,  making  ozone  and  many  other  specific 
purposes. 

(2)  Therapeutic  Uses.— Oxygen  is  largely  used  medi- 
cinally for  alleviation  in  asphyxiation,  pulmonary  complaints, 


OXYGEN  103 

etc.  ;  and  by  dentists,  in  admixture  with  nitrous  oxide,  for 
purposes  of  anaesthesia.  It  is  also  used  for  diving  operations, 
for  mine  rescue  work  (cf.  also  "  Applications  of  liquid  air," 
p.  78),  for  smoke  helmets,  and  for  aeronautical  work  at 
high  altitudes.  Its  use  has  been  suggested  for  improving 
the  atmosphere  of  theatres,  etc.,  but  at  present  the  cost  would 
be  rather  prohibitive. 

(3)  Welding  and  Cutting  of  Metals.— As  mentioned 
above,  the  principal  applications  of  oxygen  are  in  the 
welding  and  cutting  of  metals,  particularly  steel. 

(a)  Welding. — The  art  of  autogenous  welding  is  one  which 
has  been  developed  gradually  from  ancient  times.  The 
hydrogen- air,  or  the  much  more  convenient  oxy-coal  gas 
blowpipe,  was  long  used  for  lead  burning,  but  the  industry 
owes  its  present  standing  chiefly  to  the  advent  of  the  oxy- 
acetylene  blowpipe,  which  came  into  technical  use  about 
1903.  Acetylene  has  the  advantage  over  hydrogen  and  coal 
gas  of  a  considerably  higher  heat  of  combustion. 

Acetylene,  net  heat  of  combustion/ft.3     . .         815  C.H.U. 
Hydrogen,          „  „  „  „     . .         153*3     » 

Coal  gas,  ,,  ,,          „          „     . .   ca.  280       „ 

Apart  from  its  lower  heat  of  combustion  the  low  pressure 
of  coal  gas  is  a  considerable  disadvantage.  Petrol,  benzol, 
etc.,  may  also  be  used  in  conjunction  with  oxygen. 

The  equation 

2C2H2  +  502  =  4C02  +  2H20 

demands  2,\  volumes  of  oxygen  per  volume  of  acetylene,  but, 
in  practice,  the  best  results  are  found  to  correspond  to  about 
1*0  to  1-5  volumes.  This  ratio  is  in  accordance  with  the 
equation 

2C2H2  +  O2  =  2CO  +  2H2O 

and  this  represents  the  reaction  in  the  inner  white  cone 
of  the  oxy-acetylene  flame  ;  the  completion  of  the  com- 
bustion occurs  in  the  outer  cone,  this  being  relatively  cool 
and  serving  to  protect  the  weld  from  oxidation.  The  apex 
of  the  cone  has  a  temperature  of  probably  over  3000°  C. 


104  INDUSTRIAL  GASES 

There  are  two  systems  of  working — high  and  low  pressure 
respectively.  The  former  was  the  first  to  be  introduced 
and  uses  acetylene  at  about  4-7  lbs./in.2  pressure  from 
cylinders  while  the  latter  is  more  suitable  for  acetylene 
generated  directly  from  calcium  carbide.  Autogenous 
welding  of  steel,  aluminium,  etc.,  is  employed  extensively 
in  connection  with  the  motor  industry. 

(b)  Cutting. — In  1889  Fletcher  showed  that  it  was 
possible  to  cut  metals  by  introducing  excess  oxygen  into  the 
oxy-coal  gas  flame.  Twelve  years  later  Menne,  in  Germany, 
applied  the  process  to  opening  up  tuyeres  which  had  become 
blocked ;  the  process  was  found  very  convenient  and  the 
method  gradually  became  of  greater  applicability.  In  the 
early  stages  difficulty  was  experienced  from  the  lack  of  fluidity 
of  the  iron  oxide,  the  cutting  being  rendered  intermittent. 

About  1904,  however,  on  the  introduction  of  the  cutting 
blowpipe  (by  the  Soc.  Anon.  1'Oxhydrique  Internat.  of 
Belgium),  the  essential  feature  of  which  was  the  provision 
of  a  separate  conduit  for  the  "  cutting  "  oxygen,  either  in 
the  centre  of  the  heating  jet  or  behind  it,  these  difficulties 
were  overcome. 

The  method  of  operating  is  first  to  heat  up  a  corner  of 
the  article  to  be  cut  with  a  normal  flame  and  then  to  turn  on 
the  "  cutting  "  oxygen,  when  combustion  of  the  iron  com- 
mences. The  fine  "  cutting  "jet  has  sufficient  force  to  blow 
away  the  iron  oxide,  as  it  is  formed,  a  thin,  regular  cut 
resulting.  By  means  of  special  guides  for  the  blowpipe  it 
is  possible  to  make  a  very  precise  cut. 

As  in  welding,  acetylene  gives  the  best  results,  although 
operations  may  be  conducted  with  hydrogen  or  even  with 
coal  gas.  The  proportions  of  combustible  gas  required  for 
the  actual  cutting  are  as  follows  : — 

Acetylene    . .     25-10 

^    -  per  100  volumes 

Coal  gas      . .     50-20  , 

TT   j  °f  oxygen 

Hydrogen    . .  150-80 

according  to  the  thickness  of  the  work. 

The  purity  of  the  oxygen  used  is  of  great  importance  on 


OXYGEN 


105 


account  of  the  diluent  effect  of  impurities  such  as  nitrogen 
or  argon.  For  cutting  operations  a  purity  of  at  least  98  % 
is  desirable  ;  95  %  gives  decidedly  inferior  results,  although 
quite  good  for  welding.  According  to  the  International 
Oxygen  Company,  the  effect  of  the  presence  of  9  %  nitrogen 
is  to  double  the  time  of  cutting,  while  i  %  increases  the  cost 
of  cutting  by  about  25  %.  It  is  obvious  that  the  presence 
of  a  little  hydrogen  in  electrolytic  oxygen  is  no  disadvantage 
from  this  point  of  view. 

Some  idea  of  the  efficiency  of  the  process  may  be  gathered 
from  the  following  data  (Murray,  Thorpe's  "Dictionary  of 
Applied  Chemistry,"  1912),  relating  to  the  cutting  of  nickel- 
chrome  armour  plate — 


Thickness  of 
armour  plate. 

Time  per 
foot  cut. 

Oxygen  used 
per  foot. 

Oxygen  used 
per  hour. 

(in.) 

(rain.) 

(ft.3) 

(ft.3) 

9| 

3i 

30 

530 

12 

4i 

50 

650 

17 

5 

112 

1350 

The  advantages  of  oxygen  cutting  over  mechanical 
methods  are  particularly  marked  in  operations  of  demolition 
of  steel  structures,  e.g.  bridges  and  the  like. 

(4)  Other  Applications  of  Oxygen. — Among  other 
applications  of  oxygen  may  be  mentioned  the  following  : — 

The  use  of  pure  oxygen  has  been  proposed  (Pictet,  F.P. 
475528/14)  in  the  manufacture  of  water  gas.  By  passing 
a  mixture  of  steam  and  oxygen  into  the  centre  of  the  charge, 
it  is  possible  to  obtain  continuous  operation  as  opposed  to 
the  usual  intermittent  procedure.  The  employment  of 
oxygen  for  opening  refractory  tap-holes  and  blocked  tuyeres, 
has  already  been  mentioned.  Experiments  have  been  made 
on  the  operation  of  Bessemer  converters  with  pure  oxygen, 
while  the  introduction  of  oxygen  into  fluid  glass  is  found 
beneficial. 

Oxygen  is  also  used,  mostly  on  a  small  scale,  for  increasing 
the  temperature  of  furnaces  (cf.  also  "  Oxygen-enriched  air  "). 


io6  INDUSTRIAL   GASES 

Oxygen  is  used  for  the  fusion  of  platinum  ingots  (usually 
in  conjunction  with  hydrogen),  and  also  for  the  fusion  and 
manipulation  of  transparent  quartz  glass.  The  use  of  oxygen 
for  producing  high  power  lights,  e.g.  in  admixture  with  oil 
gas  or  coal  gas,  with  or  without  mantles,  has  been  tried  but 
has  not  proved  a  commercial  success.  Similarly,  proposals 
have  been  put  forward  for  the  addition  of  oxygen  to  increase 
the  working  pressures  of  internal  combustion  engines. 

There  are  many  patents,  e.g.  Farbwerke,  vorm.  Meister 
lyucius  and  Briining  (B.P.s  15948/11  and  13842/13),  dealing 
with  the  use  of  oxygen  in  connection  with  the  conversion 
of  oxides  of  nitrogen  (particularly  in  the  liquid  form)  into 
concentrated  nitric  acid.  According  to  their  D.R.P.  249329, 
compressed  oxygen  is  employed.  The  use  of  oxygen  in 
bleaching  is  said  to  give  good  results,  effecting  a  saving  in 
bleaching  powder.  Milk  can  be  sterilized  by  exposure  in  the 
fresh  condition  to  some  5  atmospheres  pressure  of  oxygen 
for  several  hours.  Similarly,  oxygen  is  used  in  the  manu- 
facture of  oxidized  oils,  having  the  advantage  that  the  process 
can  be  effected  at  a  steam  heat,  and  that  no  "  driers  "  are 
required  ;  also  for  the  artificial  maturing  of  spirits,  in  the 
production  of  vinegar,  etc.  It  is  claimed  (Valon)  that  by 
the  addition  of  oxygen  (about  OT  %)  instead  of  air,  the 
elimination  of  sulphuretted  hydrogen  from  coal  gas  by  the 
usual  iron  oxide  purifiers  is  greatly  facilitated.  Dilution 
with  nitrogen  is  avoided  (which  is  important  when  the 
gas  is  used  as  an  illuniinant  with  ordinary  batswing 
burners),  and  the  capacity  of  the  ore  for  taking  up  sulphur 
is  increased  to  75  %  of  its  weight  of  sulphur  instead  of 
50  %. 

The  Vickers  process  of  case-hardening  steel  consists  in 
effecting  a  sudden  local  heating  of  the  surface  of  the  steel  by 
means  of  an  oxy-acetylene  flame,  on  the  removal  of  which 
the  heated  layer  is  quenched  by  the  body  of  cold  metal 
underneath. 

Oxygen-enriched  Air. — There  are  a  number  of  appli- 
cations of  oxygen  to  technical  processes  in  which  even  approxi- 
mate purity  of  the  oxygen  is  a  matter  of  small  importance 


OXYGEN  107 

or  possibly  undesirable  ;  it  will  be  preferable  to  deal  with  such 
applications  under  the  heading  of  oxygen-enriched  air.  It 
is  probable  that  with  the  further  cheapening  of  oxygen,  many 
new  industrial  applications  of  this  character  will  present 
themselves.  Among  such  uses  may  be  mentioned  the 
following : — 

(1)  Use  of  oxygen- enriched  air  in  the  blast  furnace. — Trials 
have  been  carried  out  by  Trasenster  at  Ougree-Marihaye, 
Belgium   (Engineering,   (1913),  374),  with  a  blast  furnace 
supplied  with  air  of  23  %  oxygen  content  instead  of  the  normal 
21  %.     As  a  result,  a  diminution  of  5  %  in  the  coke  con- 
sumption and  an  increase  of   10-15  %  in  the  output  were 
experienced,  the  cast  iron  being  of  excellent  quality  and  rich 
in  silicon. 

The  oxygen  was  supplied  by  three  Claude  plants,  each  of 
capacity  70,000  ft.3  oxygen/hr.  Johnson  (Metall.  and  Chem. 
Eng.,  13,  (1915),  483)  found  that  an  increase  of  the  oxygen 
content  to  50  %  resulted  in  a  fuel  economy  of  33  %  when 
using  a  cold  blast  as  against  the  normal  dry  hot  blast.  The 
economy  is  still  greater  in  the  manufacture  of  ferro-silicon, 
where  a  higher  temperature  is  required. 

(2)  The  use  of  oxygen-enriched  air  in  the  arc  process  for 
nitrogen  fixation. — It  has  been  found  that  by  raising  the 
oxygen  content  to  50  %  the  yield  of  nitric  acid  in  the  above 
process  can  be  increased  from  500  kilos./K.W.Yr.  to  625 
kilos./K.W.Yr.,  the  cost  of  the  oxygen  being  more  than 
balanced  by  the  increased  production.     Some  workers  have 
found  as  much  as  50  %  increase  in  efficiency.     It  is  necessary 
to  work  with  a  closed  cycle,  as  only  about  3  %  conversion 
takes  place  under  the  most  favourable  circumstances. 

(3)  The  use  of  oxygen-enriched  air  in  the  Hausser  process. — 
This  process  depends  on  the  production  of  oxides  of  nitrogen 
by  the  explosion  of  a  compressed  mixture  of  air  and  a  fuel 
gas.     By  increasing  the  oxygen  content  of  the  air  to  about 
26  %  the  yield  of  oxides  of  nitrogen  is  raised  from  6*4  Ibs. 
to  10  Ibs.  per  1000  ft.3  of  the  combustible  gas.    According 
to  these  experiments  (at  Wendel  in  Germany)  it  was  expected, 
with  a  supply  of  7350  ft.3/hr.  of  coke  gas,  to  make  about  i  ton 


io8  INDUSTRIAL  GASES 

of  nitric  acid  per  diem,  by  the  addition  of  about  2500  ft.3 
oxygen  per  hour.  See  also  this  series  Partington,  "  The 
Alkali  Industry/'  p.  174  et  seq. 

(4)  Other  applications  of  oxygen- enriched  air. — The  use  of 
oxygen-enriched  air  has  also  been  proposed  in  the  oxidation 
of  ammonia  to  nitric  acid  by  the  Ostwald  process  ;  in  the 
oxidation  and  absorption  of  the  oxides  of  nitrogen  resulting 
from  this  and  other  operations,  and  in  the  manufacture  of 
sulphur  trioxide  by  the  contact  process. 

Estimation  and  Testing  of  Oxygen. — Oxygen  is  readily 
recognized  when  present  even  in  small  quantities  in  other 
gases.  If  present  in  hydrogen  its  estimation  is  perhaps  best 
effected  by  means  of  the  so-called  "  Grisoumeter  "  by  the 
action  of  a  red-hot  platinum  wire.  The  contraction  is  equal 
to  three  times  the  volume  of  the  oxygen  present.  For  an 
automatic  oxygen  detector  on  this  principle  cf.  Greenwood 
and  Zealley,  loc.  cit.  When  the  oxygen  is  present  in  a  non- 
combustible  gas,  or  where,  for  various  reasons,  the  use  of  a 
Grisoumeter  is  undesirable,  the  oxygen  is  readily  determined 
by  absorption  by  copper  gauze  in  the  presence  of  ammonium 
hydroxide  and  ammonium  carbonate,  by  pyrogallol,  by  sticks 
of  phosphorus,  or  by  sodium  hydrosulphite. 

The  copper  gauze  method  is  very  convenient,  an  absorp- 
tion pipette  taking  up  large  quantities  of  oxygen  without 
agitation  ;  after  the  absorption  the  gas  is  freed  from  ammonia 
before  measurement.  If  present  in  the  gas.  carbon  monoxide 
is  also  absorbed  by  this  reagent.  When  using  phosphorus 
the  temperature  must  not  be  below  15°  C.  or  oxidation  does 
not  occur  readily  ;  the  presence  of  certain  gases  has  a  similar 
inhibitive  effect.  The  use  of  pyrogallol  also  has  some 
disadvantages  as,  under  certain  conditions,  carbon  monoxide 
is  evolved  by  the  reagent. 

Sodium  hydrosulphite — used  in  weakly  alkaline  solution — 
is  an  energetic  absorbent  for  oxygen  and  is  free  from  the 
drawbacks  of  the  other  absorbents  mentioned  ;  it  does  not 
absorb  carbon  monoxide.  When  present  in  small  quantities, 
oxygen  may  be  estimated  colorimetrically  by  the  red  color- 
ation produced  in  a  solution  of  pyrogallol  or  a  mixture  of 


OXYGEN  109 

pyro-catechine,    ferrous    sulphate    and    alkali    in    aqueous 
solution  (Binder  and  Weinland,  Ber.,  (1913),  255). 

The  purity  of  commercial  oxygen  is  best  determined  by 
absorption  with  one  of  the  above  mentioned  absorbents, 
e.g.  sodium  hydrosulphite,  and  measurement  of  the  small 
residue.  Small  quantities  of  carbon  dioxide  are  readily 
determined  by  absorption  with  caustic  soda,  while  hydrogen 
may  be  estimated  by  the  Grisoumeter  method. 


REFERENCES   TO  SECTION  II. 

Engelhardt,  "  The  Electrolysis  of  Water  "  (Richards).  Easton,  Pa., 
1904. 

Murray,  "  On  the  Mechanical  Appliances  Employed  in  the  Manufacture 
and  Storage  of  Oxygen  (Baryta  Process),"  Proc.  Inst.  Mech.  Eng.,  (1890), 

131- 

Richardson,  "  Autogenous  Welding."    London,  1913. 


SECTION  III.— NITROGEN 


Properties  of  Nitrogen. — Nitrogen  is  a  colourless,  odour- 
less and  tasteless  gas,  the  most  important  physical  properties 
of  which  will  be  found  in  Table  1 2,  pp.  53  -5.  The  solubility 
in  water  is  given  in  the  following  table : — 


Temperature  °C. 

o 

IO 

15 

20 

40 

C.c.    of    gas    (measured   at 

N.T.P.)    dissolved    by    i 

c.c.    of    water    under    a 

0-0239     0-0196 

0-0179 

0-0164 

0*0118 

pressure   of    I    atm.    ex- 

clusive of  water  vapour. 

The  variation  of  the  mean  specific  heat  with  temperature 
has  been  found  by  Holborn  and  Henning  (Annalen,  (4),  18, 
(1905),  7139;  23,  (1907),  809)  to  follow  the  expression 
Cp  =  0*2350  +  0-000019^  between  o°  and  1400°  C.  According 
to  Crofts  (Chem.  Soc.  Trans.,  (1915),  290),  Cy  =0-1677 -J- 
o '000014^,  where  Cp  is  the  mean  specific  heat  between  t  and 

15-5°  c. 

Liquid  nitrogen  is  very  mobile  and  quite  colourless,  with 
a  refractive  index  (/XD)  of  1-2053  a^  "the  boiling  point.  Its 
specific  heat  is  0*43.  For  other  properties  see  Tables  12  (B) 
and  12  (C). 

Nitrogen  is  generally  regarded  as  a  very  inactive  element. 
To  a  very  considerable  extent,  by  comparison  with  such 
gases  as  oxygen,  this  is  true,  since  very  few,  if  any,  reactions 
are  known  in  which  nitrogen  enters  into  combination  at  the 
ordinary  temperature.  Given,  however,  the  stimulus  of  high 
temperatures  or  of  catalysts,  nitrogen  is  capable  of  forming 
directly  a  great  number  of  compounds.  Thus,  the  endo- 
thermic  compound  nitric  oxide  can  be  produced  by  heating 
air  to  very  high  temperatures,  and  then  rapidly  chilling, 


NITROGEN  in 

while  the  exothermic  compound  ammonia  is  easily  formed 
at  a  moderate  temperature  in  the  presence  of  a  suitable 
catalyst,  especially  at  increased  pressures.  Nitrides  are 
formed  by  direct  combination  with  a  large  number  of  metals 
and  non-metals  at  high  temperatures. 

According  to  recent  experiments  of  Strutt,  nitrogen  can 
be  obtained  in  an  allotropic  form  known  as  "  active  nitrogen," 
by  the  passage  of  an  electric  discharge,  preferably  with 
a  condenser  and  spark  gap  in  parallel,  through  nitrogen  at  a 
pressure  of  a  few  mm.  of  mercury.  A  yellow  glow  is  set 
up  in  the  gas  and  persists  for  a  period  varying  from  several 
seconds  to  some  minutes  according  to  the  conditions ;  the 
rate  of  disappearance  of  the  glow  rises  with  increase  of 
pressure.  While  in  this  state,  the  nitrogen  has  the  property 
of  combining  in  the  cold  with  various  substances,  e.g.  with 
acetylene  to  form  hydrocyanic  acid,  or  with  liquid  mercury 
to  form  mercury  nitride.  No  combination  with  oxygen  or 
hydrogen  has  been  observed  up  to  the  present.  It  is  found 
that  perfectly  pure  nitrogen  does  not  give  the  glow,  but  its 
formation  is  induced  by  the  presence  of  minute  amounts  of 
various  impurities,  e.g.  0-013  %  oxygen,  o'ooi  %  methane, 
traces  of  sulphuretted  hydrogen,  ethylene,  etc. 

For  further  information  on  this  interesting  subject, 
cf.  Strutt,  Chem.  Soc.  Trans.,  (1918),  200,  and  previous  papers, 
also  lyowry,  Trans.  Faraday  Soc.,  9,  (1913),  189. 

MANUFACTURE  OF  NITROGEN 

General. — The  production  of  nitrogen  is  a  subject  of 
great  and  increasing  importance  at  the  present  time,  chiefly 
in  connection  with  the  various  synthetic  processes  for  the 
fixation  of  atmospheric  nitrogen.  In  describing  this  subject 
it  will  be  unnecessary  to  make  more  than  a  passing  allusion 
to  such  methods  as  depend  on  a  direct  separation  of  the 
constituents  of  the  atmosphere,  either  by  chemical  or  physical 
means,  since  obviously  all  that  has  been  said  with  reference 
to  such  methods  under  oxygen,  applies  also  to  the  case  of 
nitrogen ;  moreover,  no  extensive  use  appears  to  have 


H2  INDUSTRIAL  GASES 

been  made  of  such  methods,  with  the  notable  exception  of 
the  liquid  air  process. 

(1)  By  the  Fractionation  of  Liquid  Air.— The  manu- 
facture of  nitrogen  by  this  method,  which  is  the  only  process 
worthy  of  consideration  at  the  present  time,  if  approximately 
pure  nitrogen  be  required  in  large  quantities,  has  already  been 
fully  described  (pp.  81  et  seq.). 

(2)  By  Direct  Chemical  Removal   of    the  Oxygen 
from  Air. — The  processes  coming  under  this  heading  may  be 
divided  into  two  classes  :  (a)  those  depending  on  the  alternate 
absorption  and  disengagement  of  oxygen  ;  (b)  those  involving 
the  absorption  of  oxygen  with  the  formation  of  an  oxidized 
compound  which  may  be  regenerated  subsequently  without 
the  production  of  free  oxygen. 

(a)  Practically  all  that  has  been  said  under  "  Manufacture 
of  Oxygen,"  Section  II.,  applies  equally  to  nitrogen.    The 
Brin  process  was  the   most  important,  but  the  nitrogen 
(cf.  Price,  B.P.  14213/03)  does  not  appear  ever  to  have  been 
collected  and  purified  technically. 

(b)  The  only  process  which  has  had  any  important  industrial 
application  is  that  depending  on  the  use  of  metallic  copper, 
but  as  many  interesting  reactions  are  involved  a  few  of  the 
numerous  patents  may  be  mentioned  here. 

We  find  reference  to  the  preparation  of  nitrogen  by  passing 
air  over  heated  iron  sponge  as  early  as  1869  (Spencer,  B.P. 
3752/69).  The  use  of  copper  turnings  was  proposed  by  e.g. 
Welton,  B.P.  2559/79.  Franke  and  Finke  (B.P.  10718/12) 
used  copper  gauze,  which  was  subsequently  reduced  by 
methyl  alcohol  or  water  gas.  According  to  the  Cyanid- 
gesellschaft  (D.R.P.  218671/12),  two  concentric  retorts  are 
employed  for  this  purpose,  the  charge  of  one  undergoing 
oxidation,  while  that  of  the  other  is  being  reduced,  heat- 
interchange  thus  being  effected. 

On  similar  lines  is  the  process  of  the  New  York  Nitrogen 
Co.  (B.P.  17666/11)  for  removing  the  oxygen  by  means  of 
molten  lead.  The  use  of  sulphur  (Blagburn,  B.P.  25535/08) 
or  phosphorus  (Haddan,  B.P.  24293/95)  has  also  been 
suggested.  Other  inventors  have  protected  the  use  of  wet 


NITROGEN  113 

methods,  e.g.  Wise  (B.P.  4359/77)  passes  air  over  iron 
filings  moistened  with  ferrous  sulphate  solution,  and  Alder 
(B.P.  1004/80)  uses  moist  barium  sulphide,  etc.  Similarly 
Knecht,  Perl  and  Spence  in  B.P.s  25532/11  and  25533/11, 
make  nitrogen  in  the  course  of  dissolving  cellulose  in  aqueous 
ammonia  and  cupric  hydroxide,  while  Elektrizitatswerk 
I,onza,  A.  G.  (D.R.P.  362671/16)  passes  air  through  a  hot 
solution  of  ammonium  sulphite. 

The  "  Harcourt  "  method  of  passing  a  mixture  of  air  and 
ammonia  over  heated  copper  turnings  forms  an  excellent 
means  of  preparing  nitrogen  on  a  semi- technical  scale  (cf. 
Hutton  andPetaval  (/.  Soc.  Chem.  Ind.,  (1904),  87  ;  Marston, 
B.P.  19074/1900).  It  is  important  to. use  a  considerable 
excess  of  ammonia  (about  twice  the  theoretical  quantity), 
as  otherwise,  oxides  of  nitrogen  are  formed.  After  removal 
of  ammonia,  the  nitrogen  contains  about  4  %  of  hydrogen, 
which  can  be  easily  eliminated  by  copper  oxide,  if  necessary. 
Nitrogen,  prepared  in  this  manner,  costs  about  iyj-  per 
1000  ft.3. 

In  a  series  of  patents  by  the  Farbwerke  vorm.  Meister, 
I,ucius  u.  Bruning,  the  manufacture  of  nitrogen  in  the 
oxidation  of  ammonia  is  proposed  ;  excess  of  air  is  avoided, 
nitrogen  being  obtained  after  separation  of  the  oxides  of 
nitrogen.  If  desired,  nitrogen  may  be  added  to  keep  down 
the  temperature  (B.P.s  3662/13,  28737/13,  and  9974/14). 

Of  these  methods,  the  "  copper  "  process  appears  to  be 
the  only  one  which  has  had  any  measure  of  technical  success. 
Vertical  cast-iron  retorts  are  usually  employed  to  contain  the 
copper  turnings  or  sponge  ;  the  retorts  are  heated  to  redness 
in  an  ordinary  furnace  setting  and  are  fed  alternately  with 
air  and  water  gas  or  other  reducing  medium.  Thus,  part  of 
the  plant  of  the  American  Cyanamide  Co.  is  supplied  with 
nitrogen  by  this  process,  the  reduction  being  effected  by  the 
gas  from  the  coke-oven  plant  installed  in  connection  with  the 
carbide  production  (cf . ' '  Applications  of  Nitrogen ' ') .  Accord- 
ing to  Bucher  (/.  Ind.  and  Eng.  Chem.,  9,  1917,  233),  a 
temperature  of  450°  C.  suffices  for  the  efficient  conduct  of  the 
operation,  and  a  volume  of  about  3*3  ft.3  in  the  retort 
A.  8 


ii4  INDUSTRIAL   GASES 

containing  the  copper  turnings,  gave  an  output  during  the 
oxidation  phase  of  some  200  ft.3  per  hour.  It  was  found 
important  to  guard  against  the  tendency  of  the  copper 
turnings  to  cement  together  and  block  the  gas  passage,  by 
the  provision  of  adequate  support  among  the  turnings. 

Nitrogen  results,  in  a  more  or  less  pure  state,  as  a  by- 
product from  a  number  of  chemical  processes,  e.g.  the 
effluent  from  the  chamber  sulphuric  acid  process,  in  the  Brin 
process,  in  the  manufacture  of  sodium  carbonate  by  the 
ammonia  soda  process  (cf.  p.  269),  and  also  in  the  manu- 
facture of  wood  pulp  by  the  sulphite  process. 

The  nitrogen  present  in  products  of  combustion  is  dealt 
with  in  the  next  section. 

(3)  From  Producer  Gas  and  Products  of  Combustion. 
— Since  air  consists  of  79  %  nitrogen,  it  is  evident  that  in  the 
combustion  of  carbonaceous  matter,  the  reaction  products, 
after  separation  of  the  water,  will  consist  in  large  proportion 
of  nitrogen  mixed  with  carbon  dioxide,  which  gas  is  very 
easily  removed,  or  with  carbon  monoxide  if  the  combustion 
be  only  partial  as  in  air  producer  gas.  It  will  be  convenient 
to  deal  separately  with  the  nitrogen  in  the  two  cases. 

(a)  Producer    Gas. — Air    producer   gas    contains    some 
30  %  carbon  monoxide,  the  remainder  being  mainly  nitrogen 
with  a  little  hydrogen,  methane,  etc.     A  description  will  be 
found  under  "  Manufacture  of  Hydrogen  "  (p.  205)  of  the 
production    of    hydrogen    or   mixtures    of    hydrogen    and 
nitrogen  from  producer  gas  through  the  intermediary  of 
formates. 

(b)  Products  of  Combustion. — In  this  case  we  have  a  some- 
what simpler  proposition,  the  gas  from  which  the  nitrogen 
is  to  be  isolated  consisting  of  nitrogen,  aqueous  vapour,  carbon 
dioxide,  with  probably  carbon  monoxide  or  oxygen  or  both 
and  perhaps  small  amounts  of  sulphur  compounds.    The 
removal  of  the  carbon  monoxide  and/or  oxygen,  has  attracted 
the  attention   of  a  number  of  inventors,  thus  L,ance  and 
Blworthy  (B.P.  4409/06)  complete  the  oxidation  by  passage 
over  heated  copper  oxide  ;  the  use  of  a  heated  mixture  of  a 
metallic   oxide  and  the  corresponding   metal,   e.g.   copper 


NITROGEN  115 


oxide  and  copper,  is  claimed  by  Frank  and  Caro  (B.P. 
16963/08),  serving  the  purpose  of  removing  carbon  monoxide 
and  oxygen,  either  alone  or  separately.  According  to 
Riedel  (B.P.  20631/09),  a  small  proportion  of  reducing  gas 
is  added  to  the  products  of  combustion,  the  better  to  preserve 
the  balance.  The  Braun  process,  founded  on  the  above 
patent  (cf.  B.P.  22531/1!),  is  used  on  the  large  scale  in  Berlin. 
The  Kitzinger  process,  which  is  very  similar,  is  stated  to  be 
used  especially  for  cyanamide  production  (cf.  Chem. 
Trade  J.,  62,  (1918),  88).  After  some  purification,  the 
furnace  gases  containing  a  certain  excess  of  oxygen,  are  passed 
with  producer  gas  into  a  heated  retort  where  the  oxygen  is 
removed.  The  carbon  dioxide  is  absorbed  by  passing  the 
cooled  gases  up  towers  fed  with  potash  solution,  the  potash 
being  regenerated  by  heating  the  solution  (cf.  p.  264). 
Success  is  stated  to  depend  on  an  outlet  for  the  large  quantity  ' 
of  carbon  dioxide  simultaneously  produced.  Harger  (B.P.s 
28075/11  and  16855/12)  advocates  the  use  of  a  gas  engine 
exhaust  in  order  to  secure  a  regular  combustion,  passing  the 
gases  over  a  catalyst,  e.g.  titaniferous  bog  iron  ore,  with  or 
without  use  of  the  copper-copper  oxide  mixture,  which 
may  be  employed  at  100-200°  C.  under  a  pressure  of  about 
5  atmospheres.  The  carbon  dioxide  is  removed  according 
to  various  known  methods.  Other  inventors  make  use  of 
surface  combustion  to  facilitate  exact  proportioning  of  the 
fuel  and  air,  e.g.  McCourt  and  Ellis  (B.P.  25629/12),  while 
Dreaper  (B.P.  12927/13)  adopts  similar  methods,  but 
utilizes  the  heat  in  the  cyanamide  or  cyanide  retorts  for 
which  the  nitrogen  is  being  manufactured,  cf .  also  Brownlee 
and  Uhlinger  (B.P.  5097/15). 

All  the  above  processes  are  designed  to  produce,  in  the 
first  instance,  a  mixture  of  nitrogen  and  carbon  dioxide,  the 
latter  component  being  separated  in  a  variety  of  ways.  For 
a  detailed  discussion  of  the  removal  of  carbon  dioxide  and 
other  impurities,  cf.  p.  117 ;  also  for  the  isolation  of  the 
same,  cf.  p.  264. 

(4)  By  Physical  Methods  (in  the  Gaseous  State).- 
The  eminently  successful  application  of  physical  methods  to 


u6  INDUSTRIAL   GASES 

the  separation  of  the  constituents  of  air  by  the  liquid  air  pro- 
cess, has  been  described.  For  a  discussion  of  other  physical 
methods,  cf.  " Manufacture  of  Oxygen"  (p.  94).  It  may  be 
mentioned  that  in  the  production  of  hydrogen  by  the  L,inde- 
Frank-Caro  process,  the  cooling  of  the  water  gas  to  —200°  C. 
entails  the  production  of  large  quantities  of  more  or  less 
pure  nitrogen,  about  equal  in  volume  to  the  hydrogen 
produced. 

(5)  By  Direct  Chemical  Methods.— It  should  be 
pointed  out  that  all  the  processes  thus  far  described  give,  not 
pure  nitrogen,  but  a  product  containing  a  certain  proportion 
of  argon  as  well  as  traces  of  the  other  rare  gases.  For 
example,  nitrogen  prepared  by  the  liquid  air  process  may 
contain  up  to  about  0*5  %  of  argon  ;  that  by  the  majority 
of  other  methods,  about  1*2  %.  There  are  few,  if  any, 
industrial  applications  in  which  absolute  freedom  from  argon 
is  essential.*  It  is,  however,  of  interest  to  indicate  briefly, 
possible  methods  of  securing  argon-free  nitrogen  on  a  fairly 
large  scale.  Such  nitrogen  is  easily  obtained  from  a  large 
number  of  reactions,  e.g.  from  solutions  of  ammoniacal  salts, 
by  passing  ammonia  over  heated  copper  oxide,  by  the  action 
of  sulphur  on  cyanamide  (Naef,  B.P.  14607/12),  etc. 

Purification  of  Nitrogen 

Allusion  has  been  made  in  the  preceding  pages  to  the 
elimination  of  specific  impurities  from  nitrogen.  It  will, 
however,  be  of  advantage  to  collect  together  methods  of 
dealing  with  the  different  impurities  likely  to  occur  in 
commercial  nitrogen,  either  in  large  or  small  concentrations. 

Purification  from  Carbon  Monoxide. — Although  many 
of  the  processes  detailed  under  the  Purification  of  hydrogen, 
are  equally  applicable  to  the  case  of  nitrogen,  it  is  obviously 
much  cheaper  to  effect  the  desired  operation  by  heated 

*  Argon  content  is  of  considerable  importance  in  such  cases  as  the 
synthesis  of  ammonia  where  the  reactants,  nitrogen  and  hydrogen,  are 
circulated  continuously  over  a  catalyst  in  a  closed  system.  Any  argon 
present  rapidly  accumulates  and  lowers  the  output  of  the  plant,  cceteris 
paribus,  in  proportion  to  its  concentration  and  necessitates  blowing  off  the 
gases  to  waste.  Similar  considerations  apply  in  cyanamide  production. 


NITROGEN  117 

. 

copper   oxide  (cf.  p.  114),  and  subsequent  removal  of  the 
carbon  dioxide  produced. 

Purification  from  Carbon  Dioxide. — A  full  account 
of  the  different  methods  of  removing  carbon  dioxide  in  large 
or  small  quantities  from  hydrogen,  will  be  found  on  p.  209 
(cf.  also  p.  161).  All  these  methods,  of  course,  apply  equally 
to  nitrogen. 

Purification  from  Oxygen. — The  removal  of  small 
quantities  of  oxygen  is  effected  conveniently  with  heated 
metallic  copper,  etc.  (cf.  p.  113),  or,  if  the  presence  of  a  little 
reducing  gas  is  not  detrimental,  by  the  addition  of  a  slight 
excess  of  hydrogen  or  other  reducing  gas,  and  passage  over 
a  heated  catalyst,  e.g.  platinized  pumice,  etc. 

Purification  from  Sulphur  Compounds. — In  this 
connection,  reference  may  be  made  to  the  information  given 
on  p.  210,  relating  to  the  purification  of  hydrogen.  All  these 
methods  are  applicable  to  nitrogen,  with  the  exception  of  the 
Carpenter  catalytic  hydrogenation  method. 

Comparison  of  Costs  of  Production  and  Purity 
attainable  by  the  Different  Processes 

Nitrogen  can  be  manufactured  on  a  large  scale,  say 
10,000-20,000  ft.3/hr.,  at  a  cost  (pre-war)  not  greatly 
exceeding  -/6  per  1000  ft.3  inclusive  of  capital  charges.  On 
a  smaller  scale  the  cost  of  production  will  be  higher,  say  i/- 
per  1000  ft.3.  The  copper  process  is  more  expensive. 

As  regards  purity,  reference  has  been  made  to  the  argon 
content  on  p.  116.  I/iquid  air  nitrogen  usually  contains  some 
0*5  %  oxygen  and  up  to  about  0*5  %  argon. 

Applications  of  Nitrogen — Nitrogen  Fixation 

The  only  important  industrial  consumption  of  nitrogen 
is  in  connection  with  the  fixation  of  free  nitrogen.  It  is 
scarcely  possible  to  exaggerate  the  importance  of  this  rela- 
tively new  branch  of  chemical  technology.  The  manufacture 
of  explosives  without  the  use  of  Chile  saltpetre,  has  occupied 
the  attention  of  belligerent  countries  during  the  war,  and  the 
war  would  have  been  impossible  in  Germany  but  for  the 


n8  INDUSTRIAL   GASES 

recent  advances  in  the  synthetic  production  of  ammonia  and 
nitric  acid  :  the  manufacture  of  artificial  fertilizers  in  peace 
time,  is  of  almost  equal,  if  less  sensational,  national 
importance. 

A  brief  description  will  be  given  of  the  chief  processes 
involving  the  use  of  free  nitrogen.  The  arc  process,  which 
depends  on  the  combination  of  the  constituents  of  the 
atmosphere  under  the  influence  of  a  high-tension  arc,  does 
not  necessitate  any  preliminary  separation  of  the  nitrogen 
and  oxygen. 

Nitrogen  is  sold  in  this  country  in  grey  painted  cylinders, 
under  a  pressure  of  120  atms.  ;  there  is,  as  yet,  no  great 
demand  for  nitrogen  in  this  form. 

(a)  Cyanamide  Process. — The  inception  of  this  important 
process  is  due  to  the  researches  of  Frank  and  Caro,  about 
1895.  It  depends  on  the  direct  absorption  of  free  nitrogen 
by  calcium  carbide  when  heated  to  1000-1100°  C.  Re- 
action does  not  occur  under  these  conditions  with  the  pure 
carbide,  but  proceeds  readily  with  the  commercial  product. 

CaC2  +  N2  =  Ca=N-N=C  +  C 

This  compound,  known  as  cyanamide  or  "nitrolim," 
is  stable  in  dry  air  and  is  valuable  as  a  fertilizer  ;  as  a  source 
of  ammonia,  which  is  easily  produced  by  hydrolysis  with 
steam  under  pressure  ;  in  the  production  of  cyanides,  and  in 
the  production  of  various  dye-stuffs  ;  in  the  manufacture  of 
urea  ;  in  explosives  ;  case  hardening  media,  etc. 

The  usual  method  of  effecting  the  reaction  is  to  raise 
the  temperature  of  a  relatively  small  charge  of  powdered 
calcium  carbide,  contained  in  a  lagged  closed  vessel,  to  a  high 
temperature  by  means  of  an  electrically-heated  carbon  rod, 
and  to  supply  nitrogen,  whereupon  the  exothermic  reaction 
propagates  itself  slowly  through  the  mass,  the  entire  opera- 
tion occupying  some  30-40  hours.  It  is  important  that 
the  nitrogen  should  be  free  from  water  and  oxygen,  which 
would  react  with  the  carbide  and  cyanamide  respectively. 
The  product  usually  contains  some  20  %  nitrogen ;  pure 
CaCN2  contains  35  %  nitrogen.  A  little  calcium  carbide 


NITROGEN  119 

(about  i  %)  is  usually  left  unchanged  in  the  product,  and, 
to  make  transport  safe;  is  removed  by  partial  hydration ; 
for  agricultural  purposes,  the  powder  is  oiled  to  minimize 
its  dusty  propensities.  One  of  the  chief  drawbacks  to  the 
use  of  the  cyanamide  process  in  this  country,  is  the  high 
power  consumption  as  compared  with  the  Haber  and  Cyanide 
processes  (cf.  p.  121).  -With  cheap  water  power,  on  the 
other  hand,  the  conditions  are  more  favourable.  The  first 
plant  was  erected  at  Piano  d'Orte  in  1905  ;  there  are  many 
plants  in  Norway  (particularly  at  Odda),  at  Niagara,  in 
Switzerland,  Germany,  etc. 

Some  200,000  tons  of  cyanamide  were  produced  in 
1914  ;  in  1917,  the  production  in  Germany  alone  is  stated  to 
have  been  886,000  tons  (=5400  X  io6  ft.3  nitrogen),  while 
similar  extensions  have  taken  place  in  other  countries ; 
according  to  Marselli,  the  world  production  in  1916  was 
981,500  tons  (Chem.  Trade  J.,  63,  (1918),  182). 

The  nitrogen  for  cyanamide  production  was  at  first  made 
by  the  copper  process,  but  is  now  mostly  produced  by  the 
cheaper  liquid  air  process  ;  the  American  Cyanamide  Co., 
however,  operates  part  of  its  plant  by  the  copper  process, 
the  reduction  of  the  oxide  being  effected  by  the  coke  oven 
gases  from  the  coke  plant  in  connection  with  the  carbide 
manufacture  (cf.  p.  113). 

The  cyanamide  plant  in  contemplation  by  the  American 
Air  Nitrates  Corporation  during  the  war,  was  to  produce 
350,000  tons  of  cyanamide  per  annum,  a  power  plant  of 
60,000  K.W.  being  necessary. 

(b)  The  Synthesis  of  Ammonia. — An  account  of  this 
process  will  be  given  under  the  applications  of  hydrogen. 
The  probable  consumption  of  nitrogen  for  this  purpose  in 
Germany  at  the  end  of  the  war  was  of  the  order  of  at  least 
3000  million  ft.3  per  annum  or  about  350,000  ft.3/hr.     Refer- 
ence has  already  been  made  (p.  116)  to  the  influence  of  the 
argon  content  in  this  application  of  nitrogen. 

(c)  The  Formation  of  Metallic  Nitrides.— There  are 
a  number  of  processes  for  the  production  of  different  nitrides 
by  direct  combination  of  nitrogen.     Chief  of  these  is  the 


120  INDUSTRIAL  GASES 

Serpek  process,  which  depends  on  the  action  of  nitrogen  on 
a  mixture  of  bauxite  (impure  alumina)  and  carbon  at  a 
temperature  of  about  1800°  C. 

A1203  +  3C  +  N2  =  2A1N  +  3CO 

Most  of  the  silica  of  the  bauxite  is  volatilized.  The 
process  is  carried  out  in  rotary  furnaces,  electric  resistance 
heating  being  employed ;  it  is  apparently  not  necessary  to 
use  pure  nitrogen,  air  producer  gas,  which  contains  about 
60  %  nitrogen,  being  adequate.  With  bauxite,  a  product 
containing  20-26  %  nitrogen  is  obtained,  while  pure 
alumina  gives  the  pure  nitride  containing  34  %.  The  process 
is  best  used  in  conjunction  with  the  production  from  bauxite 
of  pure  alumina  for  the  manufacture  of  aluminium  by 
electrolysis.  Thus,  the  nitride  on  decomposition  with 
alkalis  yields  ammonia  and  sodium  aluminate  if  caustic 
soda  be  employed ;  by  precipitation  of  alumina  from  the 
latter,  a  very  pure  product  is  secured. 

L,arge  scale  operations  are  being  carried  out  in  Savoy 
by  the  Societe  Generale  des  Nitrures.  A  Claude  nitrogen 
plant,  with  a  capacity  of  about  10,000  ft.3/hr.,  was  recently 
put  down  for  this  purpose.  There  are  a  number  of  patents, 
many  by  the  Badische  Anilin  &  Soda  Fabrik,  dealing  with 
the  addition  of  other  nitride-forming  substances  to  the 
alumina  and  also  with  the  use  of  other  nitrides  in  the  place 
of  aluminium  nitride. 

(d)  The  Direct  Production  of  Cyanides. — There  have 
been  many  proposals  for  the  fixation  of  nitrogen  by  the 
production  of  cyanides  ;  thus,  if  barium  carbonate  mixed  with 
carbon  be  treated  with  nitrogen  at  a  temperature  of  about 
1400°  C.,  barium  cyanide  results  and  on  treatment  with 
steam  gives  barium  hydroxide  and  ammonia.  The  only 
process,  however,  which  has  offered  any  real  prospect  of 
being  worked  on  a  large  scale  is  that  due  to  Bucher 
(loc.  cit.,  p.  113),  which  has  recently  attracted  considerable 
attention  in  the  United  States.  It  depends  on  the 
action  of  a  mixture  of  sodium  carbonate,  carbon  and  a 
small  quantity  of  iron,  which  acts  as  a  catalyst,  on  air  producer 


NITROGEN 


121 


gas  at  a  temperature  of  about  920°  C.,  with  the  production 
of  sodium  cyanide. 

The  product  can  be  converted  into  ammonia  if  desired, 
with  regeneration  of  the  sodium  carbonate  and  iron. 

This  process  holds  out  promise  of  great  advantage  over 
most  of  the  other  nitrogen  fixation  processes,  on  account  of 
its  crudity  ;  no  electric  power  is  required  and  pure  nitrogen 
is  unnecessary.  On  the  other  hand,  the  necessity  of  external 
heating  of  retorts  to  the  requisite  high  temperature,  combined 
with  the  corrosive  properties  of  the  reactants  at  high  temper- 
atures, makes  transition  from  a  semi-technical  scale  to  large 
scale  working  difficult. 

(e)  The  Hausser  Process. — This  process  depends  on  the 
production  of  oxides  of  nitrogen  on  the  explosion  of  com- 
pressed fuel  gas-air  mixtures  (cf.  p.  107). 

Comparison  of  the  Power  Requirements  in  various 
Nitrogen  Fixation  Processes. — Before  leaving  the  con- 
sideration of  this  very  important  subject,  it  will  be  interesting 
to  give  some  approximate  figures  for  the  relative  power 
requirements  of  the  different  processes  described  above,  in 
terms  of  96  %  nitric  acid  as  ultimate  product.  Where 
ammonia  is  the  immediate  product,  nitric  acid  is  obtained 
by  oxidation  according  to  the  Ostwald  or  allied  processes. 


Arc  process. 

Cyanamide 
process. 

Haber  process. 

Serpek  process. 

Power  required  per") 
ton    96  %    nitric  [ 
acid.    K.W.  years] 

r8o 

0-38 

0-050 

0'2 

Cf.  Parsons,  J.  Ind.  Eng.  Chem.,  (1917),  829. 

As  regards  the  costs  of  production,  the  following  may  be 
taken  as  an  indication  of  the  relative  values  of  the  processes. 
(Norton.) 

Cost  per  ton  of  100  %  nitric  acid — 

(a)  from  Chile  nitrate  at  1914  rates         . .         . .     £20 

(b)  by  the  Arc  process  with  power  at  o'o685^./K.W.H. 

(c)  by  the  Cyanamide  process         

(d)  by  the  Haber  process £7 


122  INDUSTRIAL  GASES 

Other  Applications.  —  Considerable  quantities  of 
nitrogen,  small  in  comparison  with  the  amounts  used  in 
connection  with  the  above  processes,  are  utilized  in  the  filling 
of  "  half -watt  "  electric  lamps,  although  nitrogen  is  rapidly 
being  replaced  by  the  more  effective  argon.  The  advantage 
of  a  certain  amount  of  gas  (about  ^  atm.)  in  the  bulb  is  that 
the  filament  can  be  run  at  a  temperature  400-600°  C. 
higher,  with  consequent  marked  increased  efficiency,  without 
producing  "  blackening  "  of  the  bulb. 

Nitrogen  is  used  for  the  storage  and  transfer  from  one 
vessel  to  another  of  highly  inflammable  liquids  like  petrol. 

High  temperature  mercury  thermometers  are  filled  with 
compressed  nitrogen. 

Estimation  and  Testing  of  Nitrogen 

In  view  of  its  inertness  towards  reagents  at  the  ordinary 
temperature,  nitrogen  is  usually  estimated  by  difference, 
i.e.  by  determination  of  the  residue  after  removal  of  other 
gases.  Oxygen,  carbon  dioxide  and  carbon  monoxide  are 
readily  estimated  separately  by  the  methods  described  under 
the  individual  gases.  In  admixture  with  hydrogen  or  other 
combustible  gas,  nitrogen  is  usually  estimated  by  passing 
the  gas  over  copper  oxide  when  hydrogen,  say,  is  removed 
and  a  residue  of  nitrogen  remains.  Mixtures  with  hydrogen 
lend  themselves  well  to  physical  methods  of  analysis.  Occa- 
sionally it  is  necessary  actually  to  absorb  nitrogen  in  order 
to  determine  the  content  of  rare  gases  ;  in  such  cases,  the 
absorption  is  best  effected  by  metallic  calcium  (cf.  Sieverts, 
Z.  Elektrochem.,  22,  (1916),  15)  or  by  calcium  carbide. 

REFERENCES   TO   SECTION   III 

General. — Crossley  ,"  The  Utilization  of  Atmospheric  Nitrogen,"  Pharm.  /„ 

(1910),  329. 
Nitrogen    Fixation    in    General. — Norton,    "  Utilization   of   Atmospheric 

Nitrogen,"  Dept.  of  Commerce  and  Labour,  U.S.A.,  Special  Agents 

Series,  No.  52. 
Summers,   "  Fixation  of  Atmospheric  Nitrogen,"  Proc.  Amer.  Inst. 

Elec.  Eng.,  (1915),  337- 
Cyanamide  Production. — Landis,  "  The  Fixation  of  Atmospheric  Nitrogen," 

Met.  and  Chem.  Eng.,  13,  (1915),  213. 
Washburn,  13,  (1915),  309- 


SECTION  IV.— THE  RARE  GASES  OF  THE 
ATMOSPHERE 

General. — The  discovery  of  argon  by  the  brilliant  work 
of  Ramsay  and  Rayleigh,  has  led  to  the  rapid  development 
of  our  knowledge  of  these  minor  constituents  of  the  atmo- 
sphere. Recently  there  have  arisen  certain  applications 
which  confer  on  them  the  right  to  be  termed  "  industrial  " 
gases.  It  is  interesting  to  recapitulate  the  approximate 
volume  percentages  present  in  the  atmosphere. 

Argon  . .  . .     0-93236  % 

Neon  . .  . .     0*00181  % 

Helium  . .  .  .     0-00054  % 

Krypton  . .  .  .     0*0000049  % 

Xenon  . .  . .     0*00000059  % 

Niton  . .  .  .  i 

Thorium  emanation/  v^  mnute  amounts- 

History  of  the  Discovery  of  the  Rare  Gases. — In 

1892,  certain  discrepancies  were  noticed  by  Rayleigh  between 
"  chemical  "  nitrogen  and  nitrogen  produced  by  removal  of 
oxygen  from  the  atmosphere,  the  former  being  some  0*5  % 
lighter  than  the  latter. 

Two  years  later  Ramsay  carried  out  experiments  on  the 
treatment  of  air,  after  removal  of  oxygen,  with  heated 
magnesium  which  absorbs  the  nitrogen.  A  reduction  to 
i/8oth  of  the  original  volume  was  effected,  and  the  density 
increased  to  16*1  (O2  =  16) ;  by  further  treatment  the  density 
rose  to  19*038.  It  was  at  first  thought  that  the  new  gas, 
which  resisted  the  action  of  magnesium,  bore  the  same 
relation  to  nitrogen  as  ozone  does  to  oxygen,  but  by  gradual 
accumulation  of  evidence,  it  was  established  that  a  new 
element  had  been  isolated. 


124  INDUSTRIAL  GASES 

At  this  point,  Ramsay  and  Rayleigh  carried  out  experi- 
ments on  a  larger  scale,  with  the  method  originally  used 
by  Cavendish,  viz.  of  removing  nitrogen  by  combination 
with  the  oxygen  of  the  air  under  the  influence  of  an  electric 
discharge.  A  high-tension  arc  was  run  (using  about  800 
watts) ,  in  a  5o-litre  flask  of  which  the  inner  surface  was  washed 
by  a  continuous  fountain  of  caustic  soda  solution,  the  flask 
being  supplied  with  a  mixture  of  air  and  oxygen.  Absorption 
took  place  at  the  rate  of  about  20  litres  per  hour.  The 
process,  if  desired,  can  be  pushed  to  completion,  but  the 
final  concentration  is  better  effected  by  other  methods. 
The  above  investigators  also  employed  the  method  of  passing 
atmospheric  nitrogen  over  a  mixture  of  metallic  magnesium 
and  quicklime  (originally  used  by  Maquenne,  Comptes  Rend., 
121,  (1895),  114),  heated  to  bright  redness. 

In  1889,  it  was  found  by  Hillebrand  that  a  certain  mineral, 
Cleveite,  on  heating  evolved  a  gas  resembling  nitrogen. 
Hearing  of  this,  it  occurred  to  Ramsay  that  the  gas  might 
be  argon.  On  carrying  out  experiments,  however,  the  gas 
was  found  to  be  not  argon,  but  a  new  gas,  which  was  subse- 
quently (1894)  termed  "  helium."  Further  researches  on 
the  fractionation  of  liquid  air,  which  was  just  becoming 
available  on  a  fairly  large  scale  (cf.  p.  69),  led  to  the 
isolation  of  neon,  krypton  and  xenon. 

ARGON 

Occurrence. — Argon  is  present  to  the  extent  of  0*93  % 
in  the  atmosphere ;  it  occurs  in  mineral  springs  (e.g.  the  gases 
from  the  Wildbad  hot  springs  contain  1-56  %  argon  and 
0*71  %  helium),  in  meteorites,  and  in  a  few  rare  minerals 
such  as  malacone  (3(ZrO2.SiO2)H2O). 

Manufacture. — Reference  has  already  been  made  to 
the  preparation  of  argon  by  the  action  of  magnesium  mixed 
with  quicklime  on  atmospheric  nitrogen — it  is  important 
that  the  lime  used  should  be  free  from  hydrate  and  carbonate, 
as  otherwise  serious  explosions  may  result.  Metallic  calcium 
can  also  be  used  with  good  effect. 

A  method  which  appears  to  be  more  suited  than  most 


THE  RARE  GASES  OF  THE  ATMOSPHERE    125 

for  technical  operations  on  a  moderate  scale,  depends  on  the 
absorption  of  nitrogen  by  calcium  carbide.  According  to 
Fischer  and  Ringe  (Ber.,  41,  (1908),  2017),  cf.  also,  Fischer 
and  Hahnel,  ib.,  43,  (1910),  1435,  air  was  passed  into  an 
iron  retort  heated  to  about  800°  C.  and  containing  calcium 
carbide  mixed  with  about  10  %  calcium  chloride  which 
facilitates  the  absorption ~at  this  comparatively  low  temper- 
ature (cf.  the  "  Manufacture  of  Cyanamide,"  p.  118).  The 
nitrogen  is  absorbed  with  the  formation  of  cyanamide  while 
the  oxygen  is  partly  fixed  as  carbonate,  some  carbon  monoxide 
being  also  formed.  The  retort  was  first  exhausted,  then 
heated  up  and  air  admitted  until  no  further  absorption 
was  observed ;  the  contents  of  the  retort  were  then  circu- 
lated in  the  sequence — copper  oxide — caustic  potash- 
sulphuric  acid — phosphorus  pentoxide — pump — gas-holder — 
retort — until  absorption  was  complete.  Some  n  litres 
of  fairly  pure  argon  were  thus  made  in  two  days  with  a  charge 
of  7  kilos,  of  calcium  carbide.  The  chief  drawback  to  the 
process  is  the  fact  that  the  residue  of  carbide  +  cyanamide 
is  very  difficult  to  remove  from  the  retort. 

It  is  obvious  that  in  the  manufacture  of  cyanamide  on  the 
large  scale,  large  quantities  of  argon  must  be  produced  in  a 
concentrated  state,  particularly  if  the  nitrogen  be  prepared 
by  the  copper  process,  and  many  thousands  of  cubic  feet 
of  highly  concentrated  argon  are  sold  annually  by  the 
American  Cyanamide  Co.,  for  lamp-filling  purposes  (cf. 
Washburn,  Chem.  News,  112,  (1915),  29).  For  similar 
procedure  in  the  fixation  of  atmospheric  nitrogen  as  cyanide, 
cf.  Bucher,  B.P.  4667/13. 

Residues  from  the  synthetic  production  of  ammonia, 
and  from  direct  nitric  acid  manufacture  using  oxygen- 
enriched  air,  with  closed  circulatory  systems,  are  also  possible 
sources  of  argon.  For  the  latter  instance  cf.  Norsk  Hydro 
Elektrisk  Kvaelstofaktieselskab,  B.P.  100099/16,  according 
to  which  the  circulation  is  so  conducted  that  the  percentage 
of  rare  gases  is  maintained  at  about  10  %. 

A  convenient  method  of  making  argon  in  the  laboratory 
depends  on  the  high  argon  content  of  commercial  "  liquid 


126  INDUSTRIAL  GASES 

air  "  oxygen,  which  often  contains  some  2-3  %  argon  and 
but  little  nitrogen.  For  example,  Claude  (Comptes  Rend., 
151,  (1910),  752)  describes  apparatus  for  the  preparation 
of  argon  at  a  rate  of  about  5  litres/hr.  from  96  %  oxygen, 
passing  the  same  over  heated  copper  and  through  an  iron 
tube  containing  magnesium  and  heated  to  redness. 

On  similar  lines  is  the  patent  (F.P.  473985/14)  of  the 

Griesheim-Elektron  Co.,  according  to  which  oxygen  as  above 

is  burnt  with  the  correct  proportion  of  hydrogen  either  with 

a  flame  in  a  water-cooled  vessel,  or  in  the  presence  of  a 

catalyst,  e.g.  copper.     A  detailed  description  of  a  method 

based  on  this  process,  is  given  by  Bodenstein  and  Wachem- 

heim    (Ber.,  51,    (1918),   265).      "liquid    air"   oxygen    is 

burnt  with  hydrogen  in  a  small  quartz  combustion  chamber. 

After  cooling  to  remove  steam,  the  exit  gases  are  led  through 

a  sensitive  rate  gauge,  and  the  respective  streams  of  oxygen 

and  hydrogen  are  adjusted  to  give  the  minimum  final  gas 

stream,  indicating  that  the  proportions  are  correct.     The 

argon  is  freed  from  traces  of  oxygen  or  hydrogen  by  passing 

through  heated  copper  and  copper  oxide,  and  finally  nitrogen 

is  removed  by  an  iron  tube  containing  calcium  turnings 

heated  electrically  to  600°  C.     Even  in  the  laboratory  it 

is  possible  to  make  argon  at  a  rate  of  about  0*5  litres  per 

hour. 

For  isolating  argon  in  really  large  quantities,  the  fraction- 
ation  of  liquid  air  probably  offers  the  most  promise.     Remem- 
bering that  the  boiling  point  of  argon  lies  between  those  of 
nitrogen  and  oxygen,  it  will  be  understood  that  the  inter- 
mediate fractions  will  be  rich  on  argon,  and  various  patents 
relate   to   the    effective  separation   of    the    argon,   mostly 
depending  on  a  further  fractionation  in  a  separate  column 
(cf.  Claude,  B.P.  3326/11;  I4nde,  B.P.  24735/14;  Filippo, 
Schoonenberg    &    Naamloze    Vennootschap    Philips    Metal 
Gloelamp-fabrik,  B.P.  101860/16;  Fonda,  (Gen.  Elec.  Co.), 
U.S.P.   1211125/17;    Claude,   Comptes  Rend.,  166,    (1918), 
492).     Blockages  are  sometimes  caused  in  liquid  air  plant 
by  the  separation  of  solid  argon,  which  may  lead  to  explosions 
on  incautious  heating  to  remove  the  obstruction.     The  final 


THE  RARE  GASES  OF   THE  ATMOSPHERE    127 

concentration  of  the  argon  (e.g.  oxygen  +  20 '%  argon) 
separated  by  the  liquid  air  process  may,  of  course,  be  com- 
pleted by  any  of  the  above-mentioned  processes,  e.g.  by 
combustion  with  hydrogen. 

It  must  be  remembered  that  the  gas  referred  to  above 
as  argon,  means  in  most  cases  a  mixture  of  the  whole  of  the 
rare  gases  of  the  atmosphere.  This  obtains  with  chemical 
means,  but  when  made  from  liquid  air  a  certain  selection 
takes  place. 

As  regards  purification,  this  is  most  readily  accomplished 
by  treatment  with  metallic  calcium  or  with  lithium  (Schloe- 
sing)  for  the  removal  of  small  quantities  of  nitrogen,  and 
by  fractional  distillation  or  selective  absorption  with  cooled 
charcoal  (see  below)  for  freeing  from  the  other  rare  gases. 

Properties  and  Applications. — Argon  in  common  with 
the  other  rare  gases,  is  distinguished  from  most  other  per- 
manent gases  by  chemical  inertness,  and  by  monatomicity. 
Its  chief  physical  constants  will  be  found  on  pp.  53-55. 

According  to  Kistiakowsky  (1897),  argon  has  the  property 
of  diffusing  through  caoutchouc  some  100  times  as  fast  as 
carbon  dioxide  ;  according  to  Dewar  (1918),  however  (cf. 
p.  10),  its  rate  is  slower.  On  passage  of  the  electric 
discharge  through  the  rarefied  gas,  a  brilliant  red  colour  is 
obtained  with  continuous  current ;  the  colour  of  the  discharge 
may  be  blue,  however,  under  certain  electrical  conditions, 
e.g.  with  oscillatory  currents.  The  change  from  red  to  blue 
is  effected  when  using  a  continuous  current  by  the  incidence 
of  Herzian  waves,  and  an  argon-filled  Geissler  tube  may  be 
used  as  a  detector  for  electric  waves.  The  spectrum  is 
not  very  characteristic  except  when  the  gas  is  fairly 
pure,  and  is  thus  not  of  much  assistance  in  detecting 
the  presence  of  argon  in  nitrogen.  A  good  criterion  of  the 
purity  is  to  be  found  in  the  measurement  of  the  dielectric 
cohesion. 

Argon  shares  with  the  other  rare  gases  the  property 
of  offering  a  low  resistance  to  the  passage  of  an  electric  spark  ; 
the  value  is  increased  to  about  2j  times  by  the  presence  of 
i  %  air  or  other  impurity.  It  has  been  observed  that  at 


128  INDUSTRIAL  GASES 

low  pressures,  spluttering  of  the  electrodes  is  more  marked 
in  the  electric  discharge  in  argon  than  in  diatomic  gases, 
and  at  a  pressure  of  about  0*005-1  mm.,  argon  causes  a 
marked  Edison  effect  in  incandescent  lamps,  with  increased 
blackening.  At  higher  pressures  its  action  is  quite  different. 
Reference  has  already  been  made  to  the  use  of  nitrogen 
in  the  "  half -watt  "  metal  filament  lamp  (p.  122).  Increasing 
quantities  of  argon  are  now  being  employed,  both  alone 
and  in  admixture  with  nitrogen,  for  this  purpose.  The 
proportion  of  argon  in  admixture  with  nitrogen  for  lamp 
rilling  may  be  estimated  (Hamburger  and  Filippo,  Z.  angew. 
Chem.,  28,  (1915),  75)  by  comparing  the  vapour  pressure 
on  cooling  in  liquid  air,  with  the  pressures  shown  by  standard 
mixtures. 

NEON 

Occurrence. — Neon  occurs  with  the  other  rare  gases 
in  the  atmosphere  and  also  in  mineral  springs.  In  the 
atmosphere  it  is  present  to  the  extent  of  0*0018  %  being, 
next  to  argon,  the  chief  constituent  of  the  inert  gas  fraction. 

Isolation. — The  most  convenient  method  of  isolating 
neon  is  by  the  separation  from  air,  either  entirely  by  physical 
means  or  by  physical  treatment  of  the  residue  of  inert  gases 
produced  by  the  chemical  removal  of  the  nitrogen  and 
oxygen.  Thus,  neon  was  discovered  by  Ramsay  in  1898  by 
the  fractional  distillation  of  crude  argon. 

According  to  Claude  (B.P.  22316/09),  neon  and  helium 
are  separated  in  the  fractionation  of  liquid  air,  by  effecting 
the  further  fractionation  of  the  last  portions  of  the  nitrogen 
fraction,  i.e.  the  most  difficultly  liquefiable  portions,  which, 
still  under  pressure,  are  liquefied  in  a  spiral  cooled  by  the 
released  and  liquefied  nitrogen.  The  "  backward  return  " 
is  used  here  as  in  oxygen  and  nitrogen  production.  It  is 
possible  in  this  way  to  obtain  a  gas  containing  some  50  % 
neon. 

The  further  purification  of  the  neon  is  best  effected  by 
fractional  sorption  with  charcoal.  It  was  shown  by  Dewar 
that  at  — 100°  C.,  argon,  krypton  and  zenon  are  absorbed, 


THE  RARE   GASES   OF  THE  ATMOSPHERE    129 

while  neon  and  helium  can  mostly  be  pumped  off  (cf. 
B.P.s  13638/04,  7808/05).  By  further  treatment  at  — 180° 
C.,  the  neon  in  turn  is  mostly  absorbed,  and  nearly  pure 
helium  can  be  pumped  off.  On  warming  up  the  neon  is 
disengaged  in  a  fairly  pure  state.  The  purification  is  best 
followed  by  the  density  (cf.  Table  12 (A),  p.  53). 

Separation  from  helium  can  also  be  effected  by  cooling 
in  liquid  hydrogen,  when  the  neon  solidifies,  while  the 
helium  (B.P.— 269°  C.)  can  be  pumped  off  (Dewar,  Roy.  Soc. 
Proc.,  67,  (1901),  329 ;  68,  (1901),  362).  According  to  Collie 
and  Patterson,  the  passage  of  an  electric  discharge  through 
hydrogen  is  accompanied  by  the  formation  of  traces  of  neon. 
Measurement  of  the  dielectric  cohesion  is 'a  good  test  of  the 
purity. 

Properties  and  Applications. — In  the  electric  discharge 
tube,  neon  gives  a  brilliant  orange  pink  incandescence  ;  by 
means  of  the  spectrum,  the  presence  of  neon  in  0*1  c.c.  of 
air  can  be  detected.  Neon  has  a  very  low  dielectric  cohesion, 
and  is  much  less  readily  absorbed  by  the  electrodes  in  a 
discharge  tube  than  most  other  gases.  It  is  on  account  of 
these  characteristics  that  the  chief  application  of  neon 
arises,  viz.  its  use  for  the  Moore  lamp.  This  lamp  consists 
of  a  long  glass  electric  discharge  tube,  e.g.  20  ft.  in  length  and 
about  if  ins.  to  2  ins.  in  diameter,  filled  with  neon  to  a 
pressure  of  about  2  mm.  of  mercury. 

Using  a  potential  difference  of  about  1000  volts  and  a 
current  of  0^94  ampere,  a  spherical  candle  power  of  about 
1300  is  obtained.  This  is  equivalent  to  a  power  consumption 
of  072  watt/mean  spherical  candle  power,  or  0-9  including 
the  losses  in  the  transformer.  The  power  factor  is  about 
0-8.  In  order  to  minimize  the  trouble  experienced  by 
absorption  at  the  electrodes,  very  large  cylindrical  hollow 
copper  electrodes  are  used,  e.g.  6  cm.  X  2*5  cm.  By  keeping 
the  current  density  down  to  i  amp./ioo  cm.2,  a  life  of  400 
hours  or  more  can  be  obtained  (cf.  Claude,  Comptes  Rend., 
151,  (1910),  1122  ;  152,  (1911),  1377  ;  lyangmuir  and  Orange, 
Amer.  Inst.  Elec.  Eng.,  (1913),  1913, 1935)-  The  colour  effect 
can  be  corrected  by  using  contiguous  tubes  containing 
A,  9 


130  INDUSTRIAL  GASES 

hydrogen.  Using  nitrogen  in  the  discharge  tube,  some  three 
times  the  potential  difference  is  required,  and  only  one- third 
the  light  is  produced.  In  the  case  of  a  neon-filled  tube, 
the  intensity  of  the  light  is  greatly  reduced  by  the  presence 
of  nitrogen. 

Neon  is  manufactured  in  Paris  on  a  scale  sufficient  to 
fill  some  1000  tubes  of  1000  candle  power,  i.e.  about  i  ft.3 
of  neon,  per  diem.  A  liquid  air  plant  producing  1750  ft.3 
of  oxygen  per  hour,  is  stated  to  yield  some  3-5  ft.3  neon  per 
diem. 

Neon  tubes  can  be  used  for  the  detection  of  Herzian  waves. 

HELIUM 

Occurrence. — Allusion  has  already  been  made  to 
Ramsay's  discovery  of  helium  in  1894,  by  the  ignition  of 
cleveite.  Its  presence  in  other  minerals  containing  radio- 
active elements,  e.g.  uranium  and  thorium,  was  subsequently 
discovered.  Such  minerals  are  fergusonite,  samarskite, 
monazite  sand,  etc.  It  was  discovered  by  Soddy  in  1903, 
that  helium  is  a  product  of  the  disintegration  of  radio-active 
bodies,  the  alpha  particle  shot  off  in  such  disintegration 
being,  in  fact,  a  charged  helium  atom. 

The  presence  of  helium  in  minerals  has  been  the  subject 
of  much  discussion  by  workers  in  radio-activity,  the  chief 
interest  centering  round  the  physical  or  chemical  state  of  the 
helium  in  the  mineral.  Since  the  gas  is  only  slowly  expelled 
by  heating,  etc.,  the  possibility  of  chemical  combination 
seemed  not  out  of  the  question.  It  was,  however,  demon- 
strated that  practically  all  the  helium  could  be  liberated  by 
very  fine  subdivision  of  the  mineral ;  it  appears,  therefore, 
that  the  gas  is  imprisoned  in  very  fine  cavities,  under  a 
pressure  of  the  order  of  200  atmospheres. 

Helium  also  occurs  in  the  atmosphere  (isolated  by  Kayser 
in  1895),  in  the  sea,  in  meteorites,  in  the  hotter  stars,  in 
mineral  waters,  e.g.  the  gases  from  the  Bath  springs  contain 
0*12  %  helium,  and  those  from  the  Wildbad  springs  0*71  %, 
and  in  natural  gas,  which  contains  up  to  about  i  %  helium 
(cf.  Cottrell,  /.  Soc.  Chem.  Ind.,  (1919),  121  T.). 


THE  RARE  GASES  OF  THE  ATMOSPHERE    131 

Manufacture. — Probably  the  most  convenient  method 
of  preparing  helium  is  from  one  of  the  above-mentioned 
minerals.  The  elimination  may  be  effected  by  heating  the 
mineral  to  redness  in  an  iron  tube  which  has  first  been 
evacuated,  or  freed  from  air  by  displacement  with  carbon 
dioxide.  A  temperature  of  1000-1200°  C.  gives  better 
results,  a  porcelain  tube  being  used.  Alternatively,  the 
mineral  may  be  heated  with  sulphuric  acid,  which  treatment 
gives  twice  the  yield  obtained  on  heating  alone,  but  has  the 
disadvantage  of  being  very  slow  ;  or  it  may  be  fused  with 
potassium  hydrogen  sulphate  in  a  hard  glass  tube.  With  the 
sulphuric  acid  treatment,  100  grams  of  cleveite  yield  some 
500  c.c.  of  helium,  which  is  obtained  in  a  fairly  pure  state 
after  removal  of  the  carbon  dioxide.  The  cost  of  production 
in  this  way  is  about  £i  per  litre. 

Purification  from  neon  and  argon  is  described  under 
"  Neon/'  the  helium  resisting  sorption  and  liquefaction  ;  the 
charcoal  method  gives  the  best  results.  Hydrogen  may  be 
separated  in  a  similar  way  by  reason  of  its  greater  sorption 
by  charcoal  at  liquid  air  temperatures.  Nitrogen  and  hydro- 
gen may  be  removed  by  the  action  of  metallic  magnesium 
plus  quicklime  and  of  copper  oxide  respectively. 

Properties  and  Applications. — Helium  is  the  most 
difficultly  liquefiable  of  all  known  gases,1  and  was  first 
liquefied  by  Kammerlingh  Onnes  (Comptes  Rend.,  147, 
(1908),  421),  the  requisite  cooling  being  effected  by  the 
evaporation  of  liquid  hydrogen  under  reduced  pressure. 

Under  the  influence  of  the  electric  discharge,  a  brilliant 
yellow  incandescence  is  obtained.  As  in  the  case  of  argon, 
a  helium  discharge  tube  may  be  used  for  the  detection  of 
electric  waves  (Dora,  Annalen,  [4],  16,  (1905),  784). 

Next  to  hydrogen,  helium  is  the  lightest  gas  known,  the 
weight  of  one  litre  at  N.T.P.  being  0-1785  gram.  The  use 
of  helium  for  filling  balloons  has  been  proposed  on  account 
of  its  non-inflammability  and  its  high  lifting  power,  which 
is  92  %  of  that  of  hydrogen  (cf.  p.  233).  Other  advan- 
tages are  the  possibility  of  increasing  the  buoyancy  by 
electrical  or  other  heating,  and  the  lower  rate  of  diffusion 


132  INDUSTRIAL   GASES 

through  the  balloon  fabric.  During  the  war,  a  process  of 
isolation  of  helium  from  natural  gas  by  fractional  distillation, 
has  been  worked  out  in  America.  It  is  stated  that  plants 
have  been  erected  with  an  output  of  50,000  ft.3/day  of  93% 
helium,  at  a  cost  of  about  £20  per  1000  ft.3  (Chem.  Trade 
/.,  64,  (1919),  99;  Nature,  102,  (1919),  487;  Cottrell,  loc. 
cit.,  p.  130). 

KRYPTON  AND  XENON 

Occurrence. — Krypton  and  xenon  were  discovered  by 
Ramsay  in  the  dregs  from  some  30  litres  of  liquid  air.  They 
are  present  in  very  small  proportions  in  the  atmosphere 
(cf.  Table  15),  also  in  mineral  springs,  mine  gases,  etc. 

Isolation  and  Properties. — Krypton  and  xenon  are 
most  conveniently  isolated  by  the  method  proposed  by 
Dewar  (Roy.  Soc.  Proc.,  68,  (1901),  362),  which  depends  on 
the  fractional  condensation  of  these,  the  most  easily  conden- 
sible  of  the  permanent  gases  of  the  atmosphere.  A  tube 
packed  with  glass  wool  is  cooled  in  liquid  air,  and  air  drawn 
through  at  a  sufficiently  reduced  pressure  to  prevent  conden- 
sation of  other  constituents.  Krypton,  xenon  and  a  little 
argon  are  deposited  on  the  glass  wool  in  the  solid  form. 
The  two  elements  can  be  separated  owing  to  the  difference 
in  their  vapour  pressures  at  the  temperature  of  liquid  air, 
krypton  17  mm.,  xenon  0*17  mm.  ;  the  former  can  thus  be 
pumped  off,  leaving  the  xenon.  Charcoal  may  be  employed 
at  about  —120°  C.  in  a  similar  manner  (Valentier  and 
Schmidt,  Sitzungsber.  Kgl.  Preuss.  Akad.  Wiss.,  38,  (1905), 
816). 

Under  the  influence  of  the  electric  discharge,  krypton 
gives  a  pale  violet  and  xenon  a  sky-blue  colour.  There  are 
at  present  no  special  applications  for  these  gases. 

Niton 

Radium  emanation  or  niton  represents  the  first  stage  in 
the  disintegration  of  radium,  and  has  been  shown  to  belong 
to  the  group  of  inert  monatomic  gases,  having  all  the 
characteristics  of  a  true  gas.  It  is  present  in  minute  amount 
in  the  atmosphere,  together  with  thorium  emanation.  It 


THE  RARE  GASES  OF   THE  ATMOSPHERE    133 

is  slowly  converted  into  helium  with  increase  to  three  times 
its  original  volume,  its  "  period  of  decay  "  (to  half  value) 
being  3*8  days. 

Niton  exhibits  a  characteristic  spectrum,  like  the  other 
rare  gases.  Owing  to  its  radio-active  nature,  niton  is  used 
to  a  considerable  extent,  though  necessarily  in  very  minute 
quantity,  in  the  treatment  of  cancer,  etc.  For  further 
details  of  this  interesting  element,  reference  must  be  made 
to  works  on  radio-activity. 


REFERENCES   TO  SECTION  IV. 

Ramsay,  "  Gases  of  the  Atmosphere."     London,  1905. 
Briscoe,  "Textbook  of   Inorganic  Chemistry."  Friend,  Little,   Turner 
and  Briscoe.     Vol.  i.     London,  1914. 


SECTION  V.— OZONE 

Occurrence. — Ozone  occurs  in  minute  quantities  in  the 
atmosphere,  particularly  in  the  upper  strata.  This  distri- 
bution can  be  explained  by  the  action  of  ultra-violet  light, 
which  is  known  to  produce  ozone,  and  which  is  largely 
absorbed  before  reaching  the  lower  layers  of  the  atmo- 
sphere. A  considerable  amount  of  work  on  this  question 
has  been  carried  out  by  Pring  (Roy.  Soc.  Proc.,  90,  A,  (1904), 
204),  who  found  that  at  an  altitude  of  7000  ft.  the  concen- 
tration was  0*00025  %  by  volume  (0^005  gram/m.3),  and 
at  11,700  ft.,  0-00047  %. 

Ozone  is  sometimes  present  in  mineral  waters,  e.g.  to  the 
extent  of  O'2  c.c. /litre  of  water. 

The  presence  of  ozone  in  the  upper  strata  of  the  atmo- 
sphere is  of  interest  in  connection  with  the  colour  of  the  sky 
on  account  of  the  blue  colour  of  ozone.  The  amount  present 
in  the  atmosphere  at  the  surface  of  the  earth,  never  exceeds 
O'ooooi  %.  Evaporation  of  water  is  operative  in  the  produc- 
tion of  small  quantities  of  ozone. 

Properties. — Ozone  is  a  permanent  gas  of  which  the 
physical  properties  will  be  found  on  pp.  53-6.  It  has  a  faint 
blue  colour  and  a  powerful  and  characteristic  odour  which 
renders  possible  its  detection  by  smell  at  a  dilution  of  the 
order  of  0-0002  %  (Pring),  while  quite  small  concentrations 
have  an  irritant  action  on  the  mucous  membrane. 

Ozone  is  an  allotropic  modification  of  oxygen,  consisting 
of  three  atoms  of  oxygen.  Its  constitutional  formula  is 
probably  O  =  O  =  O.  Its  production  from  oxygen  is  strongly 
endothermic,  thus — 

3O2  =  2O3  —  68,000  calories 
lyike  all  endothermic  gases,  ozone  is  only  stable  at  a  very 


OZONE  135 

high  temperature.  Thus,  according  to  the  Nernst  Heat 
Theorem  (Nernst,  Z.  Elektrochem.,  9,  (1903),  891),  the 
equilibrium  in  oxygen  would  be  about  10  %  at  a  temperature 
of  6640°  C.,  whereas  at  3230°  C.  the  corresponding  value  is 
i  %  and  at  2183°  C.,  0*1  %.  Consequently  ozone  is  in  a  con- 
dition of  metastability  under  ordinary  conditions.  At  the 
ordinary  temperature,  however,  the  rate  of  decomposition  is 
fairly  slow.  At  100°  C.  the  decomposition  is  relatively  rapid, 
while  at  300°  C.  it  is  practically  instantaneous.  Conversion 
into  oxygen  is  accelerated  by  the  presence  of  various  catalysts 
such  as  metallic  oxides,  chlorine,  etc.  According  to  Chapman 
and  Jones  (Chem.  Soc.  Trans.,  (1910),  2463  ;  (1911),  1811) 
the  rate  of  decomposition  is  unaffected 'by  the  presence  of 
nitrogen,  carbon  dioxide  and  possibly  water  vapour. 

As  a  consequence  of  the  above  characteristics,  ozone  has 
very  powerful  oxidizing  properties,  generally  furnishing  one 
atom  of  free  oxygen,  the  volume  remaining  constant,  e.g. 
in  the  action  on  potassium  iodide  in  solution,  with  liberation 
of  iodine — 

2KI  +  O3  +  H2O  =  2KOH  +  O2  + 12 

On  the  other  hand,  in  some  reactions,  all  three  atoms  of 
oxygen  enter  into  combination,  as,  e.g.  in  the  absorption  of 
ozone  by  turpentine  or  oil  of  cinnamon. 

In  the  presence  of  water,  ozone  attacks  many  metals. 
Thus,  the  properties  of  mercury  are  completely  modified  by 
the  action  of  a  mere  trace  of  ozone,  the  metal  becoming 
drossy,  losing  its  convex  surface  and  adhering  to  glass. 
Similarly,  most  organic  substances  are  rapidly  oxidized  ;  e.g. 
indiarubber  cannot  be  employed  in  contact  with  ozonized 
air.  Paraffin  wax  or  concentrated  sulphuric  acid  may  be 
used  as  a  lute. 

By  reason  of  its  unstable  nature,  ozone  has  never  been 
isolated  in  a  state  of  even  approximate  purity  in  the  gaseous 
state.  The  highest  concentration  which  has  been  realized 
in  the  gaseous  state,  in  oxygen,  is  some  28  %  by  weight 
(  =  22  %  by  volume).  Ladenburg  (Ber.,  31,  (1898),  2508, 
2830),  however,  by  careful  fractionation  in  the  liquid  state, 


136  INDUSTRIAL  GASES 

obtained  an  oxygen-ozone  mixture  containing  about  86  % 
ozone,  on  the  assumption  that  the  formula  is  O3. 

There  is,  however,  considerable  doubt  as  to  the  correctness 
of  this  assumption,  thus  Harries  (Ber.,  45,  (1912),  936;  Liebig's 
Annalen,  390,  (1912),  235)  considers  that  one-third  or  more 
of  the  "  ozone  "  is  really  O4  or  possibly  O6.  This  conclusion 
is  based  on  a  study  of  the  constitution  of  certain  ozonides. 
By  the  action  of  ordinary  ozone,  two  distinct  classes  of 
ozonides  are  produced,  one  of  which  corresponds  to  the 
addition  of  O4.  On  washing  the  crude  ozonized  gas  with 
dilute  caustic  soda  solution,  the  so-called  "  oxozone,"  i.e. 
O4,  C>6»  etc.,  is  removed  and  a  single  ozonide  results.  Sir 
Joseph  Thompson  has  shown  that  at  least  nine  substances 
are  formed  by  the  passage  of  an  electric  discharge  in  oxygen 
(Chem.  News,  103,  (1911),  265). 

I/iquid  ozone  has  a  dark  blue  colour,  is  not  very  mobile, 
and  is  more  magnetic  than  liquid  oxygen.  It  is  a 
dangerous  substance,  as  in  contact  with  organic  matter 
it  explodes  violently.  The  solid  substance  has  not  been 
described. 

Ozone  has  a  characteristic  spectrum,  and  its  solubility 
in  water  is  probably  of  the  same  order  as  that  of  oxygen 
(cf.  p.  93),  but  considerable  uncertainty  exists  on  this  point. 

Production  of  Ozone 

General. — The  first  recognition  of  ozone  was  by  Van 
Marum  in  1785,  while  much  of  the  classical  work  which 
determined  the  constitution  of  this  gas  is  due  to  Schonbein, 
Soret  and  Brodie.  The  difficulty  of  investigation  was 
greatly  increased  by  the  fact  that,  except  at  very  low  temper- 
atures, ozone  could  not  be  obtained  in  even  an  approximately 
pure  state. 

In  consequence  of  the  endothermicity  of  ozone,  it  is  fairly 
obvious  that  the  conditions  suitable  for  its  production 
from  oxygen  are  the  attainment  of  a  very  high  temperature 
and  then  a  rapid  freezing  of  the  equilibrium.  Ozone  is  also 
produced  in  the  liberation  of  oxygen  from  its  compounds 
at  the  ordinary  temperature. 


OZONE  137 

The  different  methods  of  producing  ozone  may  be  classified 
under  the  following  headings : — 
(a)  Chemical  methods. 
(6)  By  the  thermal  treatment  of  oxygen. 

(c)  By  electrolysis  of  aqueous  solutions. 

(d)  By  photochemical  means. 

(e)  By  the  electric  discharge  in  air  or  oxygen. 

In  connection  with  ozone  production,  it  is  usual  to 
express  the  ozone  content  of  air,  etc.,  in  terms  of  grams  of 
ozone  per  cubic  metre,  the  units  being  of  a  convenient  order 
of  magnitude.  In  some  cases,  however,  the  concentration 
is  expressed  as  one  part  in  a  certain  number  of  parts  of  air, 
and  considerable  confusion  is  due  to  the  lack  of  clearness  in 
many  instances  as  to  whether  the  basis  of  comparison  is 
weight  or  volume. 

It  is  useful  to  note  that  since  48  grams  of  ozone  have  at 
15°  C.  a  volume  of  23*6  litres,  one  gram  of  ozone  per  cubic 
metre  is  equivalent  to  ^V  %  by  volume,  and  since  one  cubic 
metre  of  air  at  15°  C.  weighs  1225  grams,  to  about  ^  %  by 
weight.  For  the  sake  of  simplicity,  the  formula  is  here 
taken  as  O3. 

(a)  By  Chemical  Methods. — Ozone  is  produced  in  small 
amount  during  the  slow  oxidation  of  phosphorus  in  moist 
air,  and  by  the  action  of  fluorine  on  water.     Better  yields 
are  obtained  by  the  treatment  of  barium  peroxide,  potassium 
permanganate  or  potassium  dichromate  with   concentrated 
sulphuric  acid.    With  permanganate,  the  action  is  dangerous 
and  should  not  be  performed  except  with  very  small  quantities. 
According  to  Malaquin  (/.  Pharm.  Chim.,  [viii.],  3,  (1911), 
329),  good  results  are  obtained  by  heating  carefully  to  60- 
70°  C.  a  mixture  of  20  grams  of  ammonium  persulphate 
and  15  grams  of  nitric  acid  of  S.G.  1*33,  in  a  flask  from  which 
the  air  has  been  displaced  by  a  current  of  carbon  dioxide. 
When  freed  from  carbon  dioxide,  the  gases  contain  some 
3-4  %  by  volume  of  ozone  and  4-4*5  %  nitrogen. 

(b)  By  Thermal  Treatment  of  Oxygen.— While,   as 
stated  ^bove,   the  equilibrium  concentration  of  ozone  in 
oxygen  is  calculated  by  Nernst  as  some  10  %  at  a  temperature 


138  INDUSTRIAL   GASES 

of  6640°  C.,  the  equilibrium  is  so  unfavourable  at  1000°  C. 
that  i  %  of  ozone  is  reduced  to  0*001  %  in  0^0007  second 
(Clement,  Annalen,  [4],  14,  (1904),  334).  Any  process 
operating  by  simple  heat  treatment  must  obviously  provide 
for  very  rapid  cooling.  Thus  the  Charpentier  process  depends 
on  the  rapid  cooling  of  a  flame  by  sudden  dilution  with  a  large 
volume  of  secondary  air  ;  it  is  claimed  that  an  ozone  concen- 
tration of  i  gram/m.3  can  be  realized  in  this  way.  By 
heating  a  Nernst  filament  immersed  in  liquid  oxygen  to  2000° 
C.  (Fischer  and  Brahmer,  Ber.,  39,  (1906),  940;  Fischer  and 
Marx,  Ibid.,  40,  (1907),  mi),  an  ozone  content  of  3*9  %  by 
weight  was  obtained. 

When  operating  with  a  Nernst  filament  in  dry  air,  some 
oxides  of  nitrogen  may  be  formed  according  to  the  conditions, 
slow  cooling  being  favourable.  Thus  with  air  linear  velocity 
of  about  16  ft./sec.  for  dry  air,  or  23  ft./sec.  for  moist  air,  both 
ozone  and  oxides  of  nitrogen  are  produced ;  below  this 
speed  only  oxides  of  nitrogen  result,  while  at  a  velocity  of 
over  100  ft./sec.,  only  ozone  is  formed.  With  a  linear  velocity 
of  206  ft./sec.,  an  ozone  concentration  of  0*23  gram/m.3 
has  been  obtained  with  a  production  of  i'28  grams/K.W.H. 
(cf.  Fischer  and  Marx,  Ber.,  39,  (1906),  2557,  3631  ;  40, 
(1907),  443  ;  Fischer,  B.P.  3692/07). 

(c)  By  Electrolysis. — For  the  production  of  ozone  by 
this  method,  the  best  yield  is  secured  by  the  use  of  dilute 
sulphuric  acid  containing  15  %  H2SO4.  The  conditions 
favouring  the  production  of  ozone  are  low  temperature  of 
the  anode  and  electrolyte,  and  a  high  current  density  at  the 
anode,  e.g.  80  amperes/cm.2,  a  not  too  easy  combination. 
Thus,  by  embedding  platinum  foil  in  glass  and  grinding  away 
so  as  to  expose  the  edge  only,  a  concentration  of  23  %  ozone 
by  weight  (16*7  by  volume)  in  the  oxygen  evolved  was 
realized  (Fischer  and  Bendixsohn,  Z.  anorg.  Chem.,  61, 
(1909),  13,  153).  In  another  series  of  experiments  the  anode 
was  coated  with  glass  except  for  a  small  slit,  and  maintained 
at  a  temperature  of  —14°  C.,  while  the  electrolyte  was  kept 
at  o°  C.  In  this  case  the  oxygen  contained  28  %  by 
weight  of  ozone  (22  %  by  volume),  and  the  yield  was  7-1 


OZONE  139 

grams/K.W.H.  (Fischer  and  Massenez,  Z.  anorg.'Chem.,b2, 
(1907),  202,  229). 

By  superimposing  an  alternating  current  on  the  usual 
direct  current,  Archibald  and  v.  Wartenberg  (Z.  Elektro- 
chem.,  17,  (1911),  812)  increased  the  concentration  of  ozone 
with  reference  to  the  oxygen  liberated  by  the  direct  current, 
to  37  %  by  volume,  the  improvement  being  due  to  the 
depolarizing  action  of  the  alternating  current,  but  dilution 
by  the  gas  liberated  by  the  alternating  current  reduced  the 
percentage  to  6  %.  With  a  greater  ratio  of  direct  current 
to  alternating  current,  the  ozone  corresponding  to  the  direct 
current  was,  in  one  case,  15  %,  that  in  the  actual  gas  mixture 

12  %. 

(d)  By  Photochemical  Means. — Ozone  is  produced  by 
the  action  of  ultra-violet  light  or  electrical  radiations  on 
oxygen,  and  as  with  the  silent  discharge  the  action  is  re- 
versible.    According  to  Pring  the  maximum  concentration 
attainable  by  the  action  of  ultra-violet  light  is  0*15  %  by 
volume,  when  using  air,  and  o'2  %  with  oxygen. 

(e)  By  the  Electric  Discharge.— The  only  method  of 
making  ozone  which  possesses  any  technical  importance, 
is  that  depending  on  the  action  of  the  so-called  "  silent 
discharge  "   on  oxygen  or   air.     On  the   other  hand,   the 
electric  spark  produces  practically  no  ozone,  as  the  gas  is 
rapidly  decomposed  by  the  spark.     The  first  form  of  ozonizer 
is  due  to  Siemens  in  1857  (wd&  infra). 

The  precise  mechanism  of  the  process  is  still  somewhat 
obscure.  It  has  been  suggested  that  the  action  is  an  effect 
of  ultra-violet  light,  and  that  the  process  is  really  a  photo- 
chemical one. 

Using  this  process,  the  efficiency  is  enhanced  by  (i) 
keeping  the  temperature  low  ;  (2)  using  oxygen  instead  of 
air ;  (3)  drying  the  air  or  oxygen  ;  and  (4)  increasing  the 
pressure.  Since  the  formation  of  ozone  from  oxygen  is 
accompanied  by  a  decrease  in  volume,  it  follows  that  an 
increase  in  pressure  is  favourable  to  ozone  production. 
The  question  is,  however,  complicated  at  pressures  above 
atmospheric  by  the  effect  of  increased  pressure  on  the 


140  INDUSTRIAL  GASES 

electric  discharge  itself.  The  result  appears  to  be  that  the 
optimum  pressure  is  about  i  atm.  The  action  is  a  reversible 
one,  and  the  highest  concentration  realized  in  this  way  at 
the  ordinary  temperature  is  about  25  %  by  weight  =  18  % 
by  volume  (cf.  also  Goldstein,  Ber.,  36,  (1903),  3042). 
Further  details  relating  to  this  process  will  be  found  below. 
By  operating  under  reduced  pressures  at  liquid  air 
temperatures,  Briner  and  Durand  (Comptes  Rend.,  145, 
(1907),  1272)  effected  a  conversion  of  99  %.  The  best  results 
were  obtained  at  a  pressure  of  100  mm.,  the  ozone  lique- 
fying out  as  it  was  produced,  with  consequent  reduction  of 
the  pressure  to  i  mm. 

MANUFACTURE  OF  OZONE 
General  Principles  of  Ozonizers 

Influence  of  the  Character  of  the  Discharge.— It 
has  been  mentioned  above  that  the  only  commercially 
important  method  of  making  ozone  is  that  depending  on  the 
action  of  the  silent  discharge.  Generally  speaking,  ozonizers 
consist  of  two  electrodes  separated  by  a  gaseous  or  solid 
dielectric,  and  maintained  at  a  potential  difference  of  the 
order  of  10,000  volts  while  a  stream  of  air  or  oxygen  is  passed 
through  the  apparatus.  Alternating  current  is  usually 
employed,  being  obtained  by  the  use  of  a  step-up  trans- 
former with  a  periodicity  up  to  500  cycles  per  second. 

According  to  Warburg  and  I,eithauser  (Annalen,  [4],  28, 
(1909),  i)  the  current  density  and  consequently  the  ozone 
production,  are  roughly  proportional  to  the  frequency. 

If  direct  current  be  employed,  the  use  of  points  on  the 
positive  electrodes,  combined  with  high  current  density, 
leads  to  the  highest  yields  with  moderate  concentrations, 
e.g.  4  grams/m.3,  while  a  reversal  of  conditions  with  a  low 
current  density  favours  the  attainment  of  high  concentrations 
e.g.  4-9  grams/m.3  (Warburg  and  L,eithauser,  Annalen,  [4], 
20,  (1906),  734). 

Broadly  speaking  there  are  three  types  of  electrodes : 
(i)  large  smooth  electrodes,  e.g.  parallel  plates  or  concentric 


OZONE 


141 


cylinders  ;  (2)  electrodes  with  points  :  and  (3)  cotnbinations 
of  (i)  and  (2). 

The  production  of  ozone  appears  to  be  proportional  to 
the  current  and  independent  of  the  voltage  (Gray,  Annalen, 
\4\,  13,  (1904),  477).  Increase  of  capacity  in  the  circuit  is 
favourable  to  ozone  production  and  large  electrode  area  and 
short  distance  of  separation  operate  in  the  same  direction. 

Influence  of  Dielectrics. — If  the  dielectric  be  air, 
the  dividing  gap  is  usually  about  13  mm.,  and  must  not  be 
decreased  below  7  mm.  (Vosmaer),  and  the  maximum 
potential  difference  used  is  about  10,000  volts.  No  apparatus 
using  air  as  dielectric  appears  to  have  had  much  success, 
and  most  modern  forms  use  glass  as  a 'dielectric,  the  regu- 
larity of  the  discharge  being  increased  and  the  danger  of 
sparking  thus  being  minimized. 

Sparking  is  very  detrimental  as  it  leads  to  decrease  of  the 
ozone  concentration  and,  moreover,  to  the  formation  of 
oxides  of  nitrogen.  With  a  single  thickness  of  1-2  mm. 
of  glass,  a  potential  difference  of  10,000  volts  may  be  used, 
while  20,000-25,000  volts  may  be  employed  with  double 
thickness.  Using  "  vitreosil "  (fused  silica),  a  potential 
difference  of  30,000  volts  is  permissible  with  a  thickness  of 
i  mm.  This  material  has  the  further  advantage  of  not 
losing  its  dielectric  properties  with  increase  in  temperature 
in  the  manner  exhibited  by  glass  (Vosmaer). 

Relation  between  Energy,  Concentration,  and  Pro- 
duction.— The  yields  obtained  in  commercial  apparatus  vary 
greatly  from  one  type  to  another,  particularly  as  the  design 
of  some  ozonizers  is  directed  towards  high  efficiency,  whereas 
that  of  others  aims  at  simplicity  and  robustness  at  the 
expense  of  output,  but  when  using  dry  air  and  keeping  the 
temperature  down,  it  may  be  taken  that  the  relation  between 
concentration  and  the  yield  per  K.W.H.  is  somewhat  as 
follows  (cf.  Brlwein,  Z.  Sauerstoff  u.  Stickstoff  Industrie, 
3,  (1911),  130,  143,  164,  181) :— 


Concentration  of  ozone. 

Grams/m3. 

i 

2 

3 

4 

5 

6 

7 

Yield.    Grams/K.W.H. 

62 

50 

36 

23 

13 

8 

5 

142 


INDUSTRIAL  GASES 


On  account  of  the  rapid  falling  off  of  the  efficiency  with 
increase  in  concentration,  the  latter  is  naturally  kept  at  as 
low  a  value  as  possible  for  the  particular  application  in 
question.  With  the  usual  commercial  concentration  of 
about  2  grams/m.3,  and  using  dry  air  with  efficient  cooling, 
the  yield  is  usually  about  40-  60  grams/K.W.H.  On 
substituting  oxygen  for  air,  the  production  increases  to 
120-180  grams/K.W.H.,  even  this  being,  of  course,  far  below 
the  theoretical  yield  corresponding  to  the  expenditure  of 
electrical  energy  (Brlwein,  loc.  cit.). 

In  comparing  the  costs  of  production  of  ozone  by  different 
ozonizers,  it  is  important  to  see  that  the  yields  given  are  ex- 
pressed in  terms  of  an  ozone  concentration  of  1-2  grams/m3. 
The  cost  of  production  from  air  is  consequently  of  the 
order  of  1/3  to  1/9  per  kilo,  ozone,  inclusive  of  overhead 
charges  with  current  at  about  o^d./K.W.H. 

Influence  of  Moisture. — The  presence  of  moisture 
in  the  air  or  oxygen  to  be  ozonized  has  a  marked  influence. 
Thus,  the  presence  of  7  mm,  of  water  vapour  (about  i  %  by 
volume)  lowers  the  production  by  about  6  %  in  the  case  of 
oxygen  and  30  %  with  air  (Warburg  and  L,eithauser, 
Annalen,  loc.  cit.}. 

Influence  of  Temperature.— The  effect  of  raising  the 
temperature  of  the  air  to  be  ozonized  from  20°  C.  to  80°  C.  is 
to  decrease  the  production  to  about  60  %  of  its  former  value 
(lyinder,  Trans.  Amer.  Inst.  Chem.  Eng.,  3,  (1910),  188), 
while  the  results  given  below  were  obtained  by  Warburg  and 
I>ithauser  (loc.  cit.)  from  ozonizer  tests  with  constant  flow. 


Temperature  °C. 

Grams  ozone  per 
ampere  hour. 

Grams  ozone/nr". 

Air  

20 
80 

467 
338 

I-76 
1*26 

Oxygen 

18 
80 

429 
425 

0-49 
0-44 

The  following  table  gives  the  relation  between  the  percent- 
age of  ozone  and  the  temperature  in  the  case  of  a  particular 
ozonizer  (not  operating  under  commercial  conditions),  the 


OZONE 


143 


conditions    otherwise    being    constant    and    oxygen    being 
used  (Beill,  Monatsh.  Ghent.,  14,  (1893),  71). 


Temperature  °C. 

-73 

-46 

—20 

o 

20 

35 

78 

IOO 

132 

Percentage  ozone 

(by  volume)  .  . 

10 

9-2 

7*9 

5*2 

4'7 

3 

i'3 

0-8 

0-3 

At  liquid  air  temperatures  complete  conversion  can  be 
realized,  the  ozone  liquefying  out  as  produced.  By  employing 
refrigeration  in  conjunction  with  an  ozonizer,  Steynis  (cf. 
lender,  loc.  cit.)  claims  to  have  secured  a  yield  of  105-250 
grams  ozone/K.W.H.,  at  a  concentration  of  4  grams/m3. 

Materials  of  Construction. — In  view  of  the  action 
of  ozone  on  steel,  etc.,  various  special  alloys  have  been  used 
in  the  construction  of  ozonizers  and  accessory  plant,  e.g. 
chrome  steel,  nichrome,  aluminium  alloys,  etc.  Shellac 
and  "  bakelite  "  also  resist  the  action  of  ozone. 

Construction  and  Production  of  the  Various 
Commercial  Types  of  Ozonizers 

As  regards  the  patent  literature  relating  to  the  manu- 
facture and  utilization  of  ozone,  the  specifications  are  so 
numerous  and  the  value  of  the  majority  so  doubtful,  that  it 
is  impossible  to  deal  with  individual  patents  in  the  present 
volume,  and  information  must  be  obtained  from  the  Abridge- 
ments of  Specifications,  Class  90,  for  British  Patents. 

The  first  ozonizer  was  introduced  by  Siemens  in  1857, 
and  is  typical  of  all  others.  In  its  original  form  it  consisted 
of  two  concentric  glass  tubes  with  tin-foil  inside  the  inner  and 
outside  the  outer  tube,  the  air  or  oxygen  being  passed  through 
the  annular  space.  A  modification  introduced  by  Berthelot 
was  the  replacement  of  the  tin-foil  by  a  liquid  conductor, 
e.g.  water,  dilute  acid,  etc. 

The  commercial  Siemens  and  Halske  system  consists 
of  6-8  glass  tubes  surrounded  by  water  in  a  cast-iron  casing. 
Aluminium  electrodes  disposed  inside  the  glass  tubes  form 
one  set  of  electrodes,  while  the  water  serves  as  the  other 
electrode.  Using  8000  to  10,000  volts,  a  yield  of  some  50 


144  INDUSTRIAL  GASES 

grams  ozone/K.W.H.  at  a  concentration  of  2*5  grams/m.3  is 
obtained. 

The  apparatus  of  the  General  Electric  Co.  is  similar  to 
the  Siemens  and  Halske,  but  instead  of  aluminium,  enamelled 
iron  is  used  for  the  inner  electrodes. 

The  older  types  of  the  Otto  system  employed  a  rotating 
central  electrode  consisting  of  aluminium  discs  in  an  iron 
cylinder  in  order  to  break  up  any  spark  discharges,  no 
dielectric  being  used;  in  the  later  forms  this  method  is 
abandoned  and  glass  is  used  as  a  dielectric. 

The  Tindal  de  Frise  system  employs  no  dielectric  and  has 
a  series  of  serrated  semicircular  aluminium  discs,  in  a  water- 
cooled  iron  trough.  To  prevent  sparking,  a  series  of  glycerol- 
water  resistances  is  included  in  the  circuit. 

In  the  Abraham-Marmier  system,  glass  plates  one  square 
metre  in  area  are  interposed  between  water-cooled  metal 
plates  connected  alternately  to  opposite  terminals.  Short- 
circuiting  through  the  cooling  water  is  prevented  by  the  use 
of  water  showers. 

The  Ozonair  system  uses  electrodes  of  aluminium  alloy 
gauze  separated  by  mica  sheets,  the  air  being  passed  between 
the  plates.  Several  pairs  mounted  in  a  case  form  a  unit. 
The  use  of  the  gauze  is  claimed  to  prevent  sparking,  while 
the  open  construction  leads  to  efficient  cooling  without  the 
use  of  water.  The  potential  difference  is  about  7000  to 
9000  volts. 

According  to  the  Howard-Bridge  system  a  glass  cylinder 
has  an  outer  aluminium  electrode  and  an  inner  concentric 
metal  tube  serving  as  electrode,  through  holes  in  which  the 
air  enters  the  ozonizer. 

The  original  Vosmaer  system  employed  no  dielectric, 
the  discharge  passing  between  a  toothed  electrode  and  a 
plate.  Sparking  was  prevented  by  the  insertion  of  a  con- 
denser in  the  electrical  circuit.  A  dielectric  is  used,  however, 
in  the  later  forms  which  consist  of  a  series  of  cells  in  a  casting 
of  grid  form,  the  separating  walls  being  lined  with  glass 
plates,  and  each  cell  enclosing  a  sharp-edged  electrode.  In 
the  units  of  joo-iooo  watts  capacity,  a  yield  of  more  than 


OZONE  145 

50   grams/K.W.H.    at   a   concentration   of   i    gram/m.3   is 
claimed. 

The  Gerard  system,  made  by  the  Westinghouse  Co., 
makes  use  of  a  double  dielectric  consisting  of  two  concentric 
glass  tubes  with  metallic  sheathings  inside  the  inner  and 
outside  the  outer  tube  respectively.  The  air  is  passed  between 
the  tubes.  Groups  of  about  10  elements  are  mounted  in 
a  tank  rilled  with  oil.  Very  high  production,  viz.  80 
grams/K.W.H.  at  a  concentration  of  3  grams/m.3,  is  claimed. 

Applications  of  Ozone 

Water  Sterilization. — Of  the  various  applications  of 
ozone,  the  sterilization  of  potable  water  is  the  most  important. 
The  problem  of  the  sterilization  of  drinking  water,  i.e.  the 
removal  of  the  bacteria,  or  at  any  rate  most  of  the  pathogenic 
ones,  can  be  solved  in  a  variety  of  ways.  Among  these  may 
be  mentioned  (i)  sand  filtration  ;  (2)  treatment  with  chlorine 
and  subsequent  removal  of  the  excess  by  means  of  sodium 
sulphite  or  other  suitable  "  anti-chlor  ";  (3)  treatment  with 
ozone  ;  and  (4)  treatment  with  ultra-violet  light.  Of  these 
sand  filtration  is  most  commonly  adopted  when  dealing  with 
waters  not  specially  contaminated.  The  use  of  chlorine,  etc., 
although  very  effective  as  regards  sterilization,  is  not  very 
suitable  for  the  preparation  of  potable  water,  except  in  special 
cases,  as  e.g.  in  the  field,  on  account  of  the  usual  residual 
taste  imparted  to  the  water.  Ultra-violet  light  has  an 
effect  on  the  water  similar  to  that  of  ozone,  but  the  ultra- 
violet light  treatment  is  useless  if  the  water  be  even  slightly 
turbid. 

Ozone  treatment  has  many  advantages  in  that  the 
slight  excess  left  in  the  water  is  unimportant  since  it  rapidly 
disappears,  also  the  taste  of  the  water  is  unaffected  either 
by  noxious  products  or  by  action  on  the  salts  to  which 
drinking  water  owes  its  pleasant  taste.  In  treating  water 
with  ozonized  air,  it  is  important  that  the  water  should  be 
free  from  suspended  matter,  from  organic  matter,  and  iron, 
as  ozone  is  used  up  thereb}r.  Some  50  %  of  any  organic 
A.  10 


146  INDUSTRIAL  GASES 

matter  is  oxidized  by  the  ozone,  all  three  atoms  of  oxygen 
participating  in  the  reaction,  while  any  organic  iron  is  con- 
verted into  ferric  hydroxide  which  separates  out  and  clogs 
up  the  plant.  The  preliminary  removal  of  ferrous  iron 
is  effected  by  aeration,  that  of  ferric  iron  is  difficult  except 
by  the  ozone  treatment,  and  it  is  therefore  often  necessary 
to  remove  the  precipitated  ferric  hydroxide  by  subsequent 
filtration  or  by  similar  treatment.  The  ozone  required 
varies  according  to  the  amount  of  organic  matter  in  the  water; 
it  may  lie  between  2  and  35  grams/iooo  galls,  of  water,  but 
averages  about  10  grams/iooo  galls. 

The  concentration  of  the  ozone  should  be  from  2  to  2*5 
grams/m.3  of  air,  although  a  concentration  of  only  i  gram/m.3 
is  sometimes  employed,  e.g.  at  St.  Maur.  It  follows  that  the 
volume  of  air  is  roughly  equal  to  that  of  the  water,  when 
ozone  is  used  in  concentration  of  2  grams/m.3,  since  10  grams 
of  ozone  are  present  in  5  m.3  =  noo  galls,  of  air.  After  the 
ozone  treatment,  only  the  harmless  bacteria  remain  in  the 
water. 

Broadly  speaking  there  are  three  main  types  of  plant 
for  the  treatment  of  water  with  ozonized  air  :  (i)  those 
operating  with  towers  filled  with  packing,  down  which  the 
water  trickles  meeting  the  ascending  current  of  ozonized  air  ; 
(2)  those  depending  on  the  use  of  a  tower  fitted  either  with 
horizontal  perforated  plates,  the  ozonized  air  and  water 
flowing  in  co-current  upwards,  or  without  baffles  and  with 
the  water  flowing  downwards  in  counter-current ;  and  (3) 
those  in  which  the  air  is  injected  in  the  form  of  small  bubbles 
into  a  rapidly  moving  column  of  water. 

In  all  cases,  the  object  is  to  effect  very  intimate  contact 
between  the  water  and  the  sparingly  soluble  ozone,  the  action 
of  which  when  once  in  solution  is  very  rapid.  Of  the  three 
systems,  (2)  probably  gives  the  most  efficient  contact.  In 
most  modern  plants,  a  combination  of  the  above  systems 
is  adopted,  the  water  being  first  put  through  a  sand 
filter. 

In  class  (i),  we  have  the  Siemens  and  Halske  and  the 
Abraham-Marmier  systems.  Towers  packed  with  stones 


OZONE  147 

or  the  like  are  employed,  and  the  unused  ozone  is  returned 
to  the  ozonizer. 

To  class  (2)  belongs  the  Siemens  de  Frise  system,  being 
a  combination  of  the  Siemens  and  Halske  ozonizer  and  the  De 
Frise  scrubber.  In  this  case,  the  ozonized  air  is  injected 
into  the  bottom  of  a  jtower  fitted  with  perforated  baffle 
plates  which  serve  to  break  up  the  air  into  small  bubbles. 
The  Vosmaer  system,  on  the  other  hand,  employs  no  baffles 
and  has  counter-current  flow.  The  Gerard  and  Tindal 
systems  are  similar  to  the  above. 

The  Otto  system  represents  class  (3),  and  depends  on  the 
emulsification  of  the  air  by  a  Korting  injector  operated  by 
the  water.  The  injector  sucks  in  the  air,  the  action  being 
completed  by  continued  contact  in  passing  down  a  vertical 
pipe,  some  15  feet  in  length.  One  objection  to  the  Otto 
system  is  the  comparatively  small  volume  of  air  taken  in, 
and  the  consequent  necessity  for  the  high  ozone  concentration 
of  3  grams/m.3.  The  Howard-Bridge  system  is  similar.  In 
the  Ozonair  system,  the  water  is  first  atomized  into  ozonized 
air  in  the  upper  part  of  a  tower  of  which  the  lower  part  is 
occupied  by  packing.  The  ozonized  air  is  injected  through 
special  nozzles  into  the  water  in  a  tank  which  is  fed  by  water 
flowing  down  the  tower,  and  then  passes  on  to  ascend  the 
tower.  After  treatment,  the  water  is  exposed  to  the  atmo- 
sphere by  flowing  down  a  series  of  steps,  in  order  to  remove 
the  excess  of  ozone. 

As  regards  power  requirements,  it  can  be  stated 
that  for  1000  galls,  of  water,  from  0*2  to  0*7  K.W.H.  is 
usually  required,  while  the  cost  (pre-war)  varies  from  \d. 
to  id.,  plus  overhead  charges,  per  1000  galls. 

There  has  been  little  application  of  the  ozone  treatment 
of  water  in  this  country,  chiefly  on  account  of  the  high  quality 
of  the  water  used  in  most  English  towns.  An  Ozonair 
plant  has,  however,  been  installed  in  Knutsford.  There  are 
many  plants  on  the  Continent  and  in  America.  A  plant 
at  Paris,  for  example,  treats  some  400,000  galls,  of  water 
per  hour. 

The  air  to  be  ozonized  is  dried  by  the  use  of  calcium 


i48  INDUSTRIAL  GASES 

chloride  or,  preferably,  by  refrigeration.  The  ozonize rs  are 
always  connected  in  parallel,  about  10,000  volts  generally 
being  used.  According  to  Vosmaer,  the  difficulty  of  packing 
materials  for  the  pumps  used  in  the  injection  of  the  ozonized 
air  is  overcome  by  the  use  of  celluloid  piston  rings. 

Portable  ozone  outfits  were  used  for  treatment  of  water 
in  the  field  by  the  Russian  Army  in  the  Russo-Japanese  war. 

Small  apparatus  for  attachment  to  any  ordinary  house- 
hold water-tap  are  on  the  market,  mostly  working  on  the 
filter  pump  (Otto)  system. 

Air  Purification. — Ozone  is  used  on  a  considerable 
scale  for  freshening  the  air  in  crowded  buildings,  underground 
railways,  hospitals,  abattoirs,  cold  stores,  etc.  It  has  also 
been  used  with  success  in  breweries  for  the  air  of  fermen- 
tation rooms,  etc.,  having  a  beneficial  effect  on  the  yeast, 
probably  due  to  the  elimination  of  adventitious  enzymes. 

On  account  of  the  irritant  properties  of  ozone,  it  is  not 
possible  to  use  concentrations  sufficiently  high  to  exhibit 
any  marked  germicidal  effect.  Thus,  bacteriological  action 
requires  a  concentration  of  about  0-5  gram/m.3,  while  the 
highest  concentration  in  which  breathing  is  tolerable  is  of 
the  order  of  O'ooi  gram/m.3.  Ozone  is,  however,  efficacious 
in  removing  the  noxious  organic  exhalations  present  in 
crowded  rooms,  much  of  the  discomfort  of  "  stuffiness " 
being  due  to  the  presence  of  these  organic  compounds.  At 
the  same  time  an  agreeable  freshness  is  imparted  to  the  air. 
For  the  best  results,  according  to  Vosmaer,  the  ozone  should 
be  present  to  the  extent  of  O'oooi  gram/m.3,  and  in  any 
case,  not  more  than  O'ooi  gram/m.3  is  permissible.  At 
such  a  low  concentration  the  yield  is  of  the  order  of  100 
grams/K.W.H. 

The  Central  L,ondon  (Tube)  Railway  is  supplied  with 
ozonized  air  by  the  Ozonair  system.  The  procedure  in  this 
case,  which  is  typical  of  similar  installations,  is  as  follows. 
The  air  is  drawn  by  a  fan  through  a  gauze  screen  filter 
moistened  with  a  spray  of  water  which  retains  dust  and  cools 
the  air.  A  small  fraction  of  the  air  is  then  dried  and  led 
through  the  ozonizer,  after  which  it  is  returned  to  the  main 


OZONE  149 

stream.  Most  of  the  plants  on  the  above  railway  treat  some 
360,000  ft.3  of  air  per  hour ;  the  cost  is  stated  to  be  17^. 
per  million  ft.3  of  air  treated  (pre-war).  Small  plants  of  20 
to  25  watts  capacity  are  made  for  use  in  rooms  of  3000  ft.3 
content. 

Chemical  Applications. — Ozone  also  finds  application 
in  the  manufacture  of  vajrious  organic  compounds,  its  function 
being  that  of  an  oxidizing  agent.  Thus,  it  is  used  on  a 
fairly  extensive  scale  in  the  manufacture  of  artificial  vanillin 
from  isoeugenol,  a  factory  at  Courbourg,  Paris,  employing  a 
100  H.P.  plant  for  making  vanillin  by  the  Verley  process. 
A  similar  plant  is  also  in  operation  at  Niagara. 

Ozone  is  employed  in  the  manufacture  of  artificial 
camphor  (Schering)  and  artificial  silk,  for  the  bleaching  of 
oils,  waxes,  sugars,  etc.,  in  the  production  of  ozonides  (e.g.  of 
caoutchouc),  scents  and  in  many  other  organic  reactions.  It 
has  been  applied  with  success  to  the  production  of  transparent 
varnish  from  linseed  oil,  also  to  the  refining  of  the  same. 

Other  Applications. — Among  miscellaneous  appli- 
cations may  be  cited  the  sterilizing  of  barrels,  the  bleaching 
of  delicate  fabrics,  etc.  The  application  of  ozonized  air  to 
the  bleaching  of  flour  has  not  been  successful  as  the  flour 
is  affected  adversely.  Ozone  has  been  tried  for  such  purposes 
as  the  ageing  of  wines,  the  maturing  of  timber,  tobacco,  etc., 
but  in  many  cases  the  success  is  doubtful.  Recent  experi- 
ments on  the  treatment  of  wounds  with  ozone  have  shown 
the  efficacy  to  be  questionable. 

Detection  and  Estimation  of  Ozone. — In  the  absence 
of  other  oxidizing  agents,  ozone  is  readily  detected  by  its 
action  on  potassium  iodine  paper  with  liberation  of  iodine 
(cf.  p.  135).  Since,  however,  other  substances  such  as 
chlorine,  oxides  of  nitrogen,  etc.,  produce  the  same  effect, 
it  is  necessary  to  have  some  means  of  discrimination. 

A  simple  method  is  to  use  paper  moistened  with  both 
potassium  iodide  and  phenolphthalein.  The  action  of 
ozone  differs  from  that  of  other  oxidizing  agents  in  that  it 
results  in  the  formation  of  potassium  hydroxide.  A  better 
selective  test  depends  on  the  use  of  moistened  tetramethyl 


150  INDUSTRIAL   GASES 

di-^tfra-aminophenylmethane    paper,     which    exhibits    the 
following  colour  reactions  : — 

Ozone violet. 

Chlorine,  bromine          . .          . .  deep  blue. 

Oxides  of  nitrogen         . .          .  .  straw  yellow. 

Hydrogen  peroxide        . .          . .  no  action. 

One  of  the  best  methods  of  estimating  quantitatively 
the  amount  of  ozone  in  air,  oxygen,  etc.,  is  by  potassium 
iodide,  with  subsequent  titration  of  the  iodine  after  acidifi- 
cation. If  other  oxidizing  agents  are  present  the  ozone  may 
be  estimated  by  repeating  the  estimation  after  passing  the 
gas  through  a  tube  heated  to  about  260°  C.,  and  then  deter- 
mining the  difference  in  the  iodine  liberation  due  to  the 
decomposition  of  the  ozone,  this  difference  giving  the 
initial  ozone  concentration. 

A  more  positive  method  consists  in  removing  the  oxides 
of  nitrogen  by  means  of  caustic  soda,  while  hydrogen  peroxide 
may  be  eliminated  by  passing  over  finely  divided  crystals  of 
chromic  acid. 

According  to  Usher  and  Rao  (Chem.  Soc.  Trans.,  (1918), 
799),  ozone  present  in  small  quantity  is  best  estimated  by 
drawing  the  air  through  (i)  chromic  acid  plus  manganese 
dioxide,  (2)  chromic  acid  alone.  In  both  cases  hydrogen 
peroxide  is  removed  and  in  (i)  nitrogen  peroxide  also  is 
eliminated ;  on  shaking  up  with  sodium  nitrite  solution 
and  subsequently  estimating  the  degree  of  conversion  into 
nitrate,  the  difference  in  the  two  cases  gives  the  ozone 
content. 

Separation  of  ozone  from  oxides  of  nitrogen  may  also 
be  effected  by  passing  into  liquid  air,  when  the  ozone  dissolves 
but  the  oxides  of  nitrogen  separate  out  as  blue  flocks. 

REFERENCES   TO   SECTION  V. 

Vosmaer,  "Ozone,  its  Manufacture,  Properties  and  Uses."  New  York, 
1916. 

Fonrobert,  "  Das  Ozon."     Stuttgart,  1916. 

Harries,  "  Untersuchungen  iiber  das  Ozon  und  seine  Einwirkung  auf 
organische  Verbindungen."  Berlin,  1916. 


OZONE  151 

Anon.,  "  The  Use  of  Ozone  for  Chemical  Research  and  Industries," 
Chem.  News,  113,  (1916),  193,  205. 

Erlwein,  "  Herstellung  und  Verwendung  des  Ozons,"  Z.jur  Stickstoff 
und  Sauerstoff  Industrie,  3,  (1911),  130. 

Ziegenberg,  "  Die  elektrische  Ozontechnik."    Leipzig,  1910. 

Perkin,  "  The  Industrial  Uses  of  Ozone,"  Nature,  88,  (1912),  551. 

Rideal,  "  Water  Supplies."    London,  1916. 

Don,  "  The  Filtration  and  Purification  of  Water  for  Public  Supply," 
Engineering,  87,  (1909),  126,  160. 

Anon.,  "  Water  Sterilization  Plant  at  St.  Petersburg,"  Engineering,  91, 
(1911),  656. 


0-0215   0-0198   0-0190   0-0184 


PART  II.— HYDROGEN,  CARBON  MONOXIDE, 
CARBON  DIOXIDE,  SULPHUR  DIOXIDE, 
NITROUS  OXIDE,  ASPHYXIATING  GASES 

SECTION  VI.— HYDROGEN 

Occurrence. — Hydrogen  is  present  in  small  amount  in 
the  atmosphere,  0*019  %  according  to  Gautier,  0-003  % 
according  to  Rayleigh,  its  origin  being  the  fermentation  of 
cellulose,  etc.,  by  anserobic  micro-organisms. 

Physical  Properties. — Hydrogen  is  a  colourless,  taste- 
less and  odourless  gas.  It  is  the  lightest  known  gas,  the 
weight  of  one  litre  at  N.T.P.  being  0*089873  gram.  The 
solubility  in  water  is  given  in  the  following  table  :— 

Temperature  °C.  . .         . .          o  10 

C.c.  of  gas  (measured  at  N.T.P.) 

dissolved  by  i  c.c.  of  water 

under  a  pressure  of  I  atm. 

exclusive  of  water  vapour. 

The  mean  specific  heat  at  constant  volume  is  given  by 
Crofts  (Chem.  Soc.  Trans.,  (1915),  290)  as— 

Cy  =  2-41  +  0-00032^ 

where  Cv  is  the  mean  specific  heat  between  t  and  15*5°  C. 

Hydrogen  does  not  show  the  preliminary  decrease,  common 
to  other  permanent  gases,  of  the  product  pv  as  the  pressure 
is  increased,  but  gives  a  continuous  increase,  the  departure 
from  constancy  being  very  considerable  at  200  atms.  (cf.  p. 
3).  Due  allowance  for  the  diminished  quantity  of  hydrogen, 
represented  by  the  expression  p/pv,  is  important  when  calcu- 
lating the  volume  of  gas  in  a  cylinder  from  the  pressure. 
Thus  a  cylinder  of  actual  volume  of  i  ft.3  only  contains 
in -8  ft.3  of  free  hydrogen  at  121  atms.  absolute  pressure  for 
a  temperature  of  16°  C.,  in  both  cases  (cf.  pp.  4,  5). 

Hydrogen  is  occluded  to  a  considerable  extent  by  many 


HYDROGEN  153 

metals,  such  as  palladium,  platinum,  iron,  cobalt,  etc. 
Palladium  has  the  property  in  the  highest  degree.  The 
volume  occluded  varies  little  with  pressure"  between  i  and 
4-6  atms.,  but  is  dependent  on  the  temperature.  Thus, 
one  volume  of  palladium  sponge  occludes  917  volumes  of 
hydrogen  at  —  50°  C.,  the  quantity  falling  off  with  rising 
temperature  to  a  minimum  of  661  volumes  at  20°  C.  and  then 
increasing  to  754  volumes  at  105°  C.  (Gutbier,  Ber.,  46,  ii., 
(1913),  1453).  Palladium  black  and  palladium  foil  show  a 
closely  similar  behaviour. 

It  was  observed  by  Holt,  Edgar  and  Firth  (Z.  physik. 
Chem.,  82,  (1913),  513)  that  palladium  may  be  either  active 
or  passive  according  to  treatment.  These  authors  conclude 
that  the  hydrogen  exists  in  two  forms,  (i)  an  adsorbed  layer 
of  high  vapour  pressure  and  easily  removed  by  evacuation, 
and  (2)  an  absorbed  fraction  irregularly  distributed  through 
the  body  of  the  metal.  The  sorption  is  accompanied  by  the 
evolution  of  4370  calories  per  gram  hydrogen,  while  the 
palladium  increases  in  volume  by  some  10  %.  In  vacuo,  at 
the  ordinary  temperature,  92-98  %  of  the  hydrogen  is 
disengaged  and  expulsion  is  complete  at  440°  C.  ;  with  foil 
most  of  the  hydrogen  is  lost  at  100°  C.  Under  high  pressure 
the  hydrogen  is  retained  even  at  a  dull  red  heat,  e.g.  Dewar 
showed  that  300  volumes  were  absorbed  at  500°  C.  under 
120  atms.  pressure  (Chem.  Soc.  Proc.,  13,  (1897),  192). 

The  solubility  of  hydrogen  in  other  metals  is  fairly 
marked,  e.g.  platinum  black  at  the  ordinary  temperature 
dissolves  no  volumes  (Mond,  Ramsay  and  Shields,  Phil. 
Trans.,  A  186,  (1895),  657),  spongy  platinum  only  a  few 
volumes,  reduced  iron  9*4  to  19*2  volumes,  reduced  cobalt 
59  to  153  volumes,  reduced  nickel  17  to  18  volumes  (Graham, 
Phil.  Mag.,  [4],  32,  (1886),  503 ;  Neumann  and  Streintz, 
Annalen,  46,  (1892),  431)  ;  cf.  also  p.  9. 

Palladium,  and  in  a  lesser  degree  platinum  and  other 
metals,  show  a  marked  permeability  to  hydrogen,  thus 
i  m.2  of  palladium  foil  of  i  mm.  thickness  permits  the  passage 
of  325  c.c.  hydrogen  per  minute  at  265°  C.,  and  of  3992  c.c. 
at  about  1000°  C.  (Graham,  Roy.  Soc.  Proc.,  16,  (1867-68), 


154  INDUSTRIAL  GASES 

422).  Similarly  platinum  foil  i'i  mm.  in  thickness  passes 
489  c.c./min./m.2  at  a  bright  red  heat.  (Graham,  Phil.  Mag., 
[4],  32,  (1866),  401.) 

On  account  of  its  high  coefficient  of  diffusion,  hydrogen 
easily  passes  through  slightly  porous  bodies,  e.g.  indiarubber 
is  markedly  permeable  to  hydrogen  (cf.  p.  10),  while  quartz 
is  appreciably  so  at  temperatures  above  1000°  C.  For 
other  properties  see  Tables  12  and  13,  pp.  53-6. 

Liquid  Hydrogen. — Hydrogen  at  ordinary  temperatures 
is  distinguished  from  most  other  gases  by  the  fact  that,  on 
expanding  without  performing  external  work,  heating  takes 
place  (cf.  p.  67).  Consequently,  in  the  production  of 
liquid  hydrogen,  the  Joule-Thomson  effect  can  only  be  realized 
after  a  preliminary  cooling.  In  the  British  Oxygen  Co.'s 
apparatus,  this  is  effected  by  passing  the  hydrogen  at  a 
pressure  of  about  200  atms.  through  (i)  a  heat-interchanger, 
(2)  coils  immersed  in  liquid  air,  (3)  coils  cooled  by  the  ebul- 
lition of  liquid  air,  and  (4)  a  second  heat-interchanger,  after 
which  expansion  takes  place.  The  unliquefied  hydrogen 
passes  back  over  the  coils,  in  counter-current  to  the  incoming 
gases,  to  the  gas-holder.  Liquid  hydrogen  was  first  obtained 
in  quantity  by  Dewar  in  1898. 

Properties. — liquid  hydrogen  is  a  colourless,  transparent 
liquid,  a  non-conductor  of  electricity  ;  it  is  the  lightest 
known  liquid,  having  a  density  of  0*070  at  the  boiling  point. 
The  surface  tension  is  1/35  that  of  water.  Specific  heat  is 
6*4.  When  evaporated  under  reduced  pressure,  solidification 
takes  place. 

In  spite  of  its  low  boiling  point,  liquid  hydrogen  is  easily 
preserved,  as  the  residual  air  in  the  Dewar  vessels  is  frozen 
out  and  the  vacuum  made  more  perfect. 

Solid  hydrogen  is  colourless,  its  melting  point  is  —258°  C., 
the  triple  point  —258°  C.  at  55  mm.  pressure,  and  the  latent 
heat  of  fusion  16  calories. 

Chemical  Properties. — At  ordinary  temperatures,  hy- 
drogen does  not  behave  as  an  active  element,  entering  into 
direct  combination  with  only  a  few  elements  and  compounds, 
e.g.  the  halogens,  and  even  then  usually  only  under  the 


HYDROGEN  155 

influence  of  light  or  of  catalysts.  On  heating,  *  hydrogen 
reacts  with  alkali  and  alkaline  earth  metals  to  give  crystalline 
compounds,  e.g.  NaH,  CaH2,  which  are  decomposed  by  water 
with  evolution  of  hydrogen. 

Mixtures  of  hydrogen  and  air  are  inflammable  within  the 
limits  74-2-4'!%  hydrogen  (cf.  p.  40). 

An  important  characteristic  of  hydrogen  is  its  power  of 
acting  as  a  strong  reducing  agent,  e.g.  in  the  reduction  of 
metallic  oxides.  Under  high  pressures  hydrogen  will 
directly  displace  many  metals  from  solutions  of  their  salts 
with  liberation  of  free  acid.  Many  reductions  depend  on 
hydrogen  being  liberated  in  the  so-called  nascent  state,  e.g.  by 
action  of  metals,  metallic  couples,  amalgams,  etc.,  on  water, 
dilute  acids  or  alkalis.  Klectrolytically  liberated  hydrogen  is 
similarly  very  active  as  a  reducing  agent  and  its  effectiveness 
is  largely  dependent  on  the  overvoltage  of  the  cathode  used. 

Hydrogen  is  also  active  in  aqueous  solution  in  the  presence 
of  spongy  or  cqlloidal  platinum,  osmium  and  the  like — thus, 
chlorate  solutions  are  reduced  (Hofmann  and  Schneider,  Ber., 
48,  (1915),  1585),  nitrates  are  converted  into  ammonia,  etc. 

Palladium  black  induces  the  combination  of  a  mixture 
of  hydrogen  and  air  so  energetically  that  incandescence  and 
inflammation  ensue. 

Sabatier  (Ber.,  44,  (1911),  84)  opened  out  a  vast  field  of 
possibilities  by  his  researches  on  organic  reductions  by 
hydrogen  in  the  presence  of  a  moderately  heated  catalyst, 
e.g.  nickel  or  platinum.  Thus,  carbon  monoxide  is  reduced 
to  methane  by  passing  over  nickel  at  250°  C.,  and  similarly, 
unsaturated  organic  compounds  such  as  oils  are  converted 
into  saturated  compounds.  Further  reference  will  be  made  to 
this  important  subject  under  "  Applications  of  Hydrogen." 

MANUFACTURE  OF  HYDROGEN— STATIONARY 

PLANTS 

General.  —  The  manufacture  of  hydrogen  occupies 
probably  the  most  interesting  place  in  the  field  of  industrial 
gas  technology  in  the  variety  of  the  methods  employed. 
The  production  of  pure  and  cheap  hydrogen,  which  is  now 


156  INDUSTRIAL  GASES 

required  for  various  recent  developments  such  as  the  synthesis 
of  ammonia  and  the  hydrogenation  of  fats,  is  a  matter  of 
very  considerable  difficulty,  and  quite  a  large  volume  of 
patent  literature  now  relates  to  this  subject. 

Most  of  the  processes  having  any  technical  importance  at 
the  present  time  start  from  coal  (or  coke)  and  water. 

In  comparison  with  gases  such  as  nitrogen  and  carbon 
dioxide  there  are  relatively  few  sources  of  hydrogen  in  the 
form  of  a  waste  product,  but  there  are  some  cases  where 
development  is  desirable,  e.g.  the  waste  hydrogen  result- 
ing from  the  electrolytic  alkali  industry  and  from  the 
manufacture  of  electrolytic  oxygen.  Further,  large  quantities 
of  hydrogen  are  liberated  in  the  manufacture  of  oxalates 
by  the  fusion  of  sawdust  or  corncobs  with  caustic  alkalis. 
During  the  war  some  of  these  sources  of  hydrogen  have  been 
tapped  for  aeronautical  purposes,  but  in  peace  times  large 
quantities  of  such  hydrogen  have  been  blown  to  waste. 

Hydrogen  is  also  produced  as  a  by-product  together  with 
carbon  dioxide  in  the  manufacture  of  synthetic  acetone  by 
the  fermentation  process  (cf.  /.  Soc.  Chem.  Ind.,  (1919),  155  T). 

MANUFACTURE  FROM  WATER  GAS — REPLACEMENT  OF 
CARBON  MONOXIDE  BY  HYDROGEN 

There  are  two  main  methods  of  effecting  the  replacement 
of  carbon  monoxide  in  water  gas  by  hydrogen — (i)  the 
continuous  catalytic  process  mainly  due  to  the  Badische 
Anilin  &  Soda  Fabrik  ;  (2)  the  Griesheim-Elektron  process  ; 
both  processes  depend  on  the  interaction  of  carbon  monoxide 
with  steam  giving  carbon  dioxide  and  hydrogen. 

Water  gas  has  the  following  approximate  percentage 
composition : — 

Hydrogen 49 

Carbon  monoxide  . .  42 

Carbon  dioxide      . .         . .       4 

Nitrogen     . .          . .         . .       4-5 

Methane      . .          . .          . .       0-5 


100 'O 


HYDROGEN  157 

The  reversible  reaction — 

CO  +  H2O  ^  CO2  +  H2  +  10,200  calories 

gives  the   so-called  water  gas  equilibrium,   provided  that 
sufficient  time  be  allowed. 

#coX 


X 


or, 


Pco_ 
Pco2 


This  equilibrium  is  dealt  with  on  p.  309,  under  "Water 
Gas." 

From  an  industrial  standpoint  the  desideratum  is  to 
convert  as  much  carbon  monoxide  as  possible  into  the  easily 
removed  carbon  dioxide,  i.e.  to  make  the  fraction  pco/Pco^ 
as  small  as  possible. 

The  variation  of  K  with  temperature  is  shown  in  the 
following  table  ;  the  higher  values  are  experimental  but  those 
below  700°  C.  are  based  on  an  extrapolation  of  the  formula 


log  K  =  -  -       +  0783  log  T  -  0-00043T 
which  fits  those  actually  observed. 


Temperature  °C. 
K  

400 
O'o6 

500 
0-16 

600 

O'32 

700 
0-58 

800 
0*90 

900 
1-25 

IOOO 

1-62 

1 

It  is  evident  that  at  comparatively  low  temperatures 
the  conditions  are  much  more  favourable  for  the  conversion 
of  carbon  monoxide  into  carbon  dioxide  than  at  high 
temperatures. 

Thus,  if  equal  volumes  of  steam  and  hydrogen  be 
present  in  the  gas  after  treatment,  a  condition  secured  by 
taking  about  1*4  volumes  of  steam  per  volume  of  water  gas, 
the  ratio 

Pco    _  -rr  PH*  _  v 

— '~ 


158  INDUSTRIAL  GASES 

The  carbon  dioxide  production  is  further  enhanced  by 
maintaining  a  high  pH2o/Pn2  ratio  up  to  a  certain  point 
above  which  the  dilution  with  steam  lowers  the  reaction 
velocity  and  output  so  much  that  the  favourable  effect  on 
the  equilibrium  is  counterbalanced. 

We  have  seen  that  a  low  temperature  is  desiiable  ;  below 
about  400°  C.,  however,  the  reaction  velocity  becomes  so 
small  that  equilibrium  cannot  conveniently  be  attained. 
Further,  it  will  be  seen  that  even  under  favourable  conditions 
the  removal  of  carbon  monoxide  cannot  be  complete. 

There  are  two  obvious  ways  of  furthering  the  carbon 
monoxide  removal  —  (i)  by  working  at  a  low  temperature,  a 
sufficiently  great  reaction  velocity  being  attained  by  the 
use  of  an  active  catalyst  ;  (2)  by  disturbing  the  normal 
water  gas  equilibrium  through  the  introduction  into  the 
system  of  an  absorbent  for  carbon  dioxide,  e.g.  lime. 

On  these  two  principles  are  based  the  processes  of  the 
Badische  Anilin  &  Soda  Fabrik  and  the  Chemische  Fabrik 
Griesheim-Blektron  respectively. 

It  is  clear  that  variation  in  the  pressure  will  be  without 
influence  on  the  equilibrium  ;  it  should  be  mentioned  that 
reaction  may  take  place  between  hydrogen  and  carbon 
monoxide  or  carbon  dioxide  in  the  absence  of  water.  When 
a  mixture  of  Itydrogen  with  carbon  monoxide  or  carbon 
dioxide  is  passed  over  reduced  nickel  at  250°  C.,  the  following 
reactions  take  place  (Sabatier  and  Senderens,  Comptes 
Rend.,  134,  (1902),  514,  689)  :— 

CO  +  3H2  =  CH4  +  H20 
CO2  +  4H2  =  CH4  +  2H2O 


giving  a  very  complete  removal  of  the  carbon  monoxide  if 
the  hydrogen  be  in  excess.  These  reactions  are  exothermic 
and  therefore  proceed  less  completely  in  the  direction  of 
methane  formation  at  higher  temperatures,  e.g.  at  500°  C.  ; 
a  certain  amount  of  methane  may  be  formed,  however, 
unless  the  catalyst  be  selected  to  favour  the  water  gas  reaction 
as  is  the  case  in  actual  practice. 


HYDROGEN  159 

(i)  B.A.M.A.G.  Continuous  Catalytic  Process 

The  main  development  of  the  continuous  catalytic 
process  is  due  to  the  Badische  Anilin  &  Soda  Fabrik,  but 
some  other  important  patents  are  included  below. 

According  to  Hembert  and  Henry,  in  B.P.  1193/84,  steam 
is  blown  through  incandescent  coke  and  the  resulting  water 
gas,  mixed  with  excess  steam,  passed  into  retorts  packed  with 
fireproof  materials,  at  a  red  heat.  Carbon  dioxide  and  hydro- 
gen are  thus  formed  and  the  former  is  subsequently  removed 
by  lime.  Similarly,  Read,  in  B.P.  3776/85,  proposes  to 
use  heated  metallic  oxides  as  catalysts.  The  carbon  dioxide 
formed  is  subsequently  removed  by  alkalis,  absorption  in 
water  under  pressure,  etc.  In  B.P.  12608/88,  Mond  and 
lyanger  prescribe  the  elimination  of  carbon  monoxide  and 
hydrocarbons  from  fuel  gases  by  passing  with  excess  steam 
over  metallic  nickel  or  cobalt  at  a  comparatively  low  tem- 
perature, namely,  350-400°  C.  with  nickel,  400-450°  C. 
with  cobalt.  Pumice  soaked  in  nickel  chloride  solution  may 
be  used.  Carbon  dioxide  is  removed  by  known  methods  and 
the  gas  is  claimed  to  be  almost  free  from  carbon  monoxide. 
F.P.  375164/06  of  the  Compagnie  du  Gaz  de  I/yons,  relates 
to  the  use  of  iron  oxide  at  600°  C.,  while  Naher  and  Mtiller, 
in  B.P.  20486/11,  propose  the  use  of  palladium — or  rhodium — 
asbestos  at  about  800°  C.  After  three  treatments  the  carbon 
monoxide  is  claimed  to  be  reduced  to  0-4  %. 

None  of  the  above  mentioned  patents  met  with  technical 
success  and  the  commercial  development  of  the  process  by 
the  use  of  active  catalysts,  as  set  forth  in  the  following  series 
of  patents,  is  due  chiefly  to  the  Badische  Co. 

According  to  B.P.  26770/12,  hydrogen  is  manufactured 
by  the  interaction  of  carbon  monoxide  and  steam  under 
pressure  in  presence  of  a  catalyst  at  a  temperature  of  e.g. 
300-600°  C.  A  pressure  of  4-40  atms.  is  used  to  accelerate 
the  reaction.  Iron  or  nickel  may  be  used  as  catalyst.  Carbon 
monoxide  is  almost  entirely  removed.  The  process  is  stated 
to  be  specially  suitable  for  gases  containing  only  little  carbon 
monoxide ;  in  such  a  case  the  enhanced  heat  regeneration 


160  INDUSTRIAL  GASES 

tinder  pressure  is  a  further  advantage  since  the  heat  evolution 
is  small.  The  use  of  pressure  does  not  appear  to  have  been 
developed  in  practice. 

B.P.  27117/12  relates  to  the  maintenance  of  the  temper- 
ature in  the  above  process  by  the  catalytic  combustion  of 
small  quantities  of  oxygen  added  to  the  gases.  Further, 
the  steam  required  for  the  reaction  may  be  thus  supplied 
if  only  a  little  carbon  monoxide  be  present.  In  B.P. 
27955/12,  a  number  of  catalysts  for  the  above  reaction 
are  described,  all  with  a  basis  of  finely  divided  iron  oxide  ; 
the  working  range  is  from  400-500°  C.  and  heating  to  over 
650°  C.  is  to  be  avoided.  B.P.  8864/13  deals  with  catalysts 
consisting  largely  of  nickel  or  cobalt ;  according  to  D.R.P. 
297258/14,  the  metals  should  be  disposed  in  small  quantities 
on  suitable  supports  and  should  be  derived  from  salts  free 
from  sulphur  and  halogens.  Further  catalysts  are  given  in 
B.P.  27963/13.  When  using  nickel  as  catalyst,  methane  is 
formed  and  it  is  here  claimed  that  such  methane  formation 
may  be  avoided  by  using  catalysts  consisting  largely  of  iron 
in  conjunction  with  nickel,  chromium,  etc.  The  catalysis 
is  very  rapid  and  suitable  also  for  small  quantities  of  carbon 
monoxide.  Working  temperatures  are  about  400-600°  C. 
B.P.  16494/14  relates  to  the  use  of  spathic  iron  ore  as  catalyst, 
heating  to  above  650°  C.  being  avoided ;  a  binding  agent, 
such  as  A1(OH)3,  may  be  added  for  briquetting  purposes. 
In  D.R.P.  284176/14,  the  use  of  the  oxides  of  rare  earths, 
especially  of  cerium  oxide,  in  conjunction  with  other  activants, 
is  recommended. 

A  different  class  of  catalyst  is  specified  by  Buchanan  and 
Maxted  in  B.P.  6476/14,  which  protects  the  use  of  lixiviated 
alkaline  ferrite.  One  passage  gives  a  gas  containing  28  % 
carbon  dioxide  and  2  %  carbon  monoxide.  In  another 
patent,  B.P.  6474/14,  the  same  inventors  propose  the  use  of 
metallic  couples  such  as  iron  +  copper,  e.g.  sodium  ferrite 
treated  with  a  copper  salt.  The  couple  is  heated  to  500°  C. 
and  a  mixture  of  carbon  monoxide  with  hydrogen  passed 
over  together  with  excess  steam.  An  iron  -j-  silver  couple  is 
stated  to  be  very  active. 


HYDROGEN  161 

The  process  founded  on  the  above  Badische  patents  is 
claimed  by  the  Berlin  Anhaltische  Maschinenbau  Aktien- 
Gesellschaft  (B.A.M.A.G.)  to  be  the  cheapest  of  all  processes 
for  making  hydrogen  on  a  very  large  scale.  It  is  used  by 
the  Badische  Co.  at  Oppau  for  the  manufacture  of  synthetic 
ammonia.  One  obvious  advantage  of  the  process  is  the 
fact  that  whereas  other  -methods  require  2-5  volumes  of 
water  gas  per  volume  of  hydrogen  produced,  little  more  than 
i 'i  volumes  are  necessary  in  this  case.  Since  water  gas  costs 
about  4^.  per  1000  ft.3  (pre-war)  the  effect  of  this  difference 
may  easily  be  estimated.  Further,  as  the  reaction  is  exo- 
thermic, it  is  easy  by  means  of  heat-interchangers  and  care- 
ful external  lagging  to  make  the  supply  of  heat  unnecessary 
except  on  first  starting  up.  A  temperature  of  400-500°  C. 
is  maintained  in  the  contact  mass;  little  attention  is  required, 
there  being  no  valves  to  operate,  and  one  man  can  look  after 
several  contact  sets.  Starting  with  water  gas  mixed  with  the 
desired  excess  of  steam — exhaust  steam  may  be  used — the 
gases  issuing  from  the  catalyst  chamber,  when  freed  from 
excess  steam  by  cooling,  have  a  percentage  composition 
somewhat  as  follows  :— 

Hydrogen        . .          . .  65 

Carbon  monoxide       . .  . .  1-2 

Carbon  dioxide           . .  . .  30 

Nitrogen,  methane,  etc.  . .  4 

The  gases  are  compressed  to  about  25-50  atms.  and  freed 
from  carbon  dioxide  by  counter-current  scrubbing  with  water 
while  under  pressure,  the  energy  of  the  water  issuing  from 
the  scrubber  being  largely  recovered  by  means  of  a  turbine. 
For  data  on  the  solubility  of  carbon  dioxide  in  water 
under  pressure,  cf.  p.  256.  Final  removal  of  the  carbon 
dioxide  may  be  effected  with  alkali  solution,  also  under 
pressure. 

On  passage  through  the  catalyst,  all  the  sulphur  com- 
pounds in  the  water  gas — which  needs  no  special  purification 
except  from  dust  and  tar — are  converted  into  sulphu- 
retted hydrogen  which  is  removed  with  the  carbon  dioxide. 

A.  II 


162  INDUSTRIAL   GASES 

If  necessary,  the  remaining  1*5-3  %  carbon  monoxide  is 
extracted  by  an  auxiliary  process. 

Plants  are  constructed  up  to  a  capacity  of  about  35,000 
ft.3  hydrogen  per  hour.  A  life  of  six  months  is  claimed  for 
the  catalyst.  Before  the  war  the  only  plant  known  to  be  in 
operation  was  that  at  the  works  of  the  Badische  Co.  It  is 
claimed  that  the  process  can  produce  hydrogen  at  the  low  cost 
of  1/9  per  1000  ft.3  (pre-war) ;  taking  into  consideration  the 
fact  that  each  volume  of  water  gas  produces  approximately 
its  own  volume  of  hydrogen,  together  with  the  continuous 
and  comparatively  simple  nature  of  the  operations,  this  would 
not  seem  improbable.  It  should  be  observed  that  the  presence 
of  some  4  %  nitrogen  is  a  serious  disadvantage  in  certain 
applications,  e.g.  in  aeronautics.  The  method  is  eminently 
suited  from  this  point  of  view  for  the  synthetic  production 
of  ammonia  ;  by  the  addition  of  air  to  the  steam  in  the 
"  make  "  period  of  the  water  gas  manufacture,  any  desired 
nitrogen-hydrogen  mixture  may  be  produced  (cf.  p.  207). 
A  certain  amount  of  methane  will  always  occur  in  hydrogen 
made  by  this  method. 

Theory  of  the  B.A.M.A.G.  Continuous  Catalytic 
Process. — Assuming  the  water  gas  to  have  the  following 
percentage  composition  : — 

Hydrogen •  50   ' 

Carbon  monoxide     . .         . .  42  v 

Carbon  dioxide         . .          . .  4 

Nitrogen        . .         . .         . .  4 

100 

and  the  temperature  of  the  catalyst  to  be  500°  C.,  it  is 
interesting  to  calculate  the  theoretical  result  of  using  100 
volumes   of    water  gas  and  300  volumes  of  steam,  both 
measured  at  the  same  temperature. 
We  then  have 

Pco  _  K  PH*  _      fi  Pnt 

I —  "•  A —  O  ID  v— 

PC02  />H20  />H20 

If  we  express  the  original  condition  of  the  gas  mixture  in 


HYDROGEN  163 

terms  of  partial  pressures  in  atmospheres,  we  have  the  follow- 
ing values  :  — 

Pu2o  ......  0750 

PH.  -.  •  -  0-125 

Pco  ••  ••  °'I05 

pco2  •  .....  o-oio 

~  .  .  .  .  o-oio 


I  '000 

The  equation 

CO+H20-H2+C02 

indicates  that  no  change  in  volume  takes  place  during  the 
reaction. 

Consequently,  if  we  take  the  change  in  partial  pressure 
of  the  carbon  monoxide  in  the  interaction  as  being  repre- 
sented by  x,  it  may  easily  be  seen  that  the  final  partial 
pressures  of  the  reactants  will  be 

Pnzo   ......  0750  -  x 

Pn2     ......  0-125+  x 

Pco     ......  0-105  -x 

Pco2    ••  ••  o-oioH-  x 

......  o-oio 


I  '000 

The  value  of  x  may  be  deduced  from  the  relationship 


#coa  X  pu2 

=  (0-105-*)  (0750-*) 
(O'OIO  +*)(0'I25  +*) 

which    gives  the  value  of  0-09899  atm.  for  x.     The  final 

partial  pressure  of  carbon  monoxide,  therefore,  is  0*006  atm. 

On  the  removal  of  the  steam  by  cooling,   the  partial 

pressure   of    the    carbon    monoxide    rises    to    —  —      atm. 

=  0-0172  atm.,  since  the  partial  pressure  of  steam  after 
reaction  is  0750—  0-099=0-651  atm.  and  the  partial  pressure 
of  the  non-condensable  gases,  in  consequence,  0-349 


164  INDUSTRIAL   GASES 

By  similar  reasoning  the  final  composition  of  the  gas  is 
seen  to  be 

Hydrogen 0-6418 

Carbon  monoxide     . .          . .  0-0172 

Carbon  dioxide         . .          . .  0*3123 

Nitrogen        . .          . .          . .  0*0287 

i -oooo 

After  removal  of  carbon  dioxide  this  becomes,  expressed  in 
percentages — 

Hydrogen  . .     93-33 

Carbon  monoxide      . .         . .       2-50 
Nitrogen          . .         . .          . .       4-17 


100-00 

(2)  Griesheim-Elektron  Process 

A  description  will  first  be  given  of  the  principal  patents 
on  which  the  process  is  based. 

In  U.S. P.  229339/80,  Tessie  du  Motay  describes  the 
production  of  hydrogen  by  passing  water  gas,  freed  from 
sulphur,  over  heated  lime.  The  method  is  elaborated  by  the 
Chemische  Fabrik  Griesheim-Elektron  in  B.P.  2523/09, 
according  to  which,  water  gas  and  steam  are  passed  over 
caustic  or  slaked  lime  at  500°  C.  in  a  suitable  container  which 
may  be  provided  with  stirring  gear.  The  reaction  is  self- 
supporting  and  the  chamber  is  cooled  to  below  the  temper- 
ature of  the  dissociation  of  calcium  carbonate — preferably 
below  500°  C.  By  the  addition  of  5  %  iron  powder  the 
reaction  is  greatly  accelerated.  The  lime  is  regenerated  by 
subsequent  calcination  of  the  calcium  carbonate.  In  a  later 
patent,  B.P.  13049/12,  it  is  claimed  that  the  lime  may  be 
advantageously  used  in  the  form  of  lumps,  the  action  not 
being  confined  to  the  surface  as  might  be  expected.  The 
material  may  thus  be  used  in  vertical  towers  and  regenerated 
in  situ.  The  same  company,  in  D.R.P.  284816/14,  describes 


HYDROGEN  165 

the  manufacture  of  hydrogen  by  the  action  of  steam  under 
about  10  atms.  pressure,  on  a  mixture  of  lime  and  charcoal 
or  lignite.  With  lime,  a  temperature  of  600-800°  C.  is 
required,  but  by  using  baryta  a  lower  temperature  is  possible. 
Among  other  patents  may  be  mentioned  B.P.  7147/13  (Soc. 
1'Air  lyiquide)  which  relates  to  the  utilization  of  the  carbon 
monoxide-rich  fraction  obtained  in  the  separation  of  carbon 
monoxide  from  hydrogen  by  the  Claude  liquefaction  process 
(cf.  p.  170).  This  gas,  which  contains  some  hydrogen,  is 
partially  or  wholly  converted  into  hydrogen  by  the  action 
of  heated  slaked  lime  as  above,  the  product  being  returned 
to  the  water  gas  to  be  liquefied. 

Bearing  on  this  reaction  there  is  a  considerable  amount 
of  literature,  a  brief  survey  of  which  now  follows. 

Merz  and  Weith  (Ber.,  13,  (1880),  718) 'describe  a  lecture 
experiment  in  which  carbon  monoxide  is  passed  over  heated 
calcium  hydroxide  just  below  a  red  heat.  Hydrogen  with 
only  a  small  percentage  of  carbon  monoxide  is  easily  obtained. 

The  matter  was  further  studied  in  Haber's  laboratory  by 
Engels  (Karlsruhe  Dissertation,  1911,  "  Uber  die  Wasserstoff 
Gewinnung  aus  Kohlenoxyd  und  Kalkhydrat  ")  who  carried 
out  extensive  experiments  on  the  reactions  underlying  the 
process.  Carbon  monoxide  was  passed  over  lime,  the 
temperature,  speed,  and  CO/H2O  ratio  being  varied.  Kngels 
concludes  that  in  the  absence  of  a  catalyst  the  conversion 
takes  place  essentially  on  the  calcium  hydroxide,  although  the 
water  gas  reaction  plays  a  minor  part.  On  the  contrary,  if 
5  %  reduced  iron  be  present,  the  action  takes  place  mainly 
in  the  gaseous  phase.  If  pure  lime  be  used  the  reaction 
velocity  is  too  low  below  500°  C.,  while  540°  C.  should  not  be 
exceeded  as  the  calcium  hydroxide  has  a  vapour  pressure  of 
I  atmosphere  at  547°  C.  ;  a  greater  steam  concentration  than 
that  corresponding  to  the  vapour  tension  of  lime  at  the 
particular  temperature  is  useless  and,  on  account  of  the  dilu- 
tion of  the  reaction  mixture,  to  be  avoided.  The  reaction 
velocity  is  increased  about  10  times  by  the  addition  of  iron  ; 
thus  with  an  81/19  H2O/H2  ratio,  a  gas  flow  of  I2'5  litres 
carbon  monoxide,  measured  at  20°  C.,  per  litre  lime  per  hour, 


166  INDUSTRIAL   GASES 

gave  at  500°  0.,  a  gas  containing  0*4  %  carbon  monoxide  in 
the  absence  of  iron,  while  under  the  same  conditions  but  using 
5  %  iron,  a  corresponding  velocity  of  138  litres  per  hour  gave 
practically  pure  hydrogen  (0*2  %  carbon  monoxide). 

According  to  Vignon  (Bull.  Soc.  Chim.,  9,  (1911),  18),  in 
treating  water  gas  with  lime  no  action  takes  place  until 
400°  C.,  when  hydrogen  is  formed  together  with  some  methane 
and  ethylene.  The  proportion  of  hydrogen  to  hydrocarbons 
increases  as  the  temperature  is  raised,  pure  hydrogen  being 
formed  at  600°  C.  lyevi  and  Piva  (Ann.  Chim.  App.,1,  (1914), 
i  ;  J.  Soc.  Chem.  Ind.,  (1914),  310)  consider  the  action  of 
carbon  monoxide  on  calcium  hydroxide  to  take  place  through 
the  intermediate  formation  of  formates  and  oxalates,  and 
state  that  on  heating  sodium  formate  in  an  atmosphere  of 
carbon  monoxide,  hydrogen  with  carbon  dioxide  and  some 
methane  is  formed.  In  a  later  paper  (Chem.  Soc.  Abstracts, 
(1916),  ii.,  525)  the  same  investigators  observe  that  the  de- 
composition temperature  of  sodium  formate  is  lowered  from 
375°  C.  to  260°  C.  by  the  presence  of  slaked  lime.  With  pure 
lime,  carbon  monoxide  gives  rise  to  formates  at  250-300°  C. 
and  to  calcium  carbonate  and  hydrogen  above  300°  C. 

Theory  of  the  Griesheim-Elektron  Process.— It  is 
instructive  to  calculate  what  is  the  lowest  possible  per- 
centage of  carbon  monoxide  which  can  be  obtained  with  a 
given  proportion  of  steam  at  say  500°  C.,  below  which 
temperature  the  reaction  velocity  is  low. 

Consider  a  gas  of  the  percentage  composition — 

Hydrogen     . .         . .  50 

Carbon  monoxide    . .         . .  42 

Carbon  dioxide        . .         . .  4 

Nitrogen 4 

100 

to  100  volumes  of  which  at  100°  C.,  200  volumes  of  steam  are 
added. 

Now,  since  the  final  volume  of  hydrogen  is  approximately 
equal  to  the  original  volume  of  the  water  gas,  the  carbon 


HYDROGEN  167 

monoxide  being  almost  completely  converted  into  hydrogen 
without  change  of  volume,  we  have  after  cooling  to  100°  C. — 

^H2/  =  CH.2i  +  VCO,  =  50  +  42  =  92 

while 

^H2o7  =  20°  —  vco.  =  200  —  42  =  158 

where  the  suffixes  i  and  /denote  the  initial  and  final  volumes 
respectively. 
Thus— 

f-=K|^=o*i6T^  =  0*093 

#CO,  />H20  158 

The  value  for  the  dissociation  pressure  of  calcium  carbonate 
as  determined  by  Johnson  (/.  Amer.  Chem.  Soc.,  32,  (1910), 
938)  is  i  mm.  at  587°  C.,  but  taking  for  simplicity  i  mm.  at 
the  lower  temperature  of  500°  C., 

pco  =0*093  pc02  =  0*093  mm.  approximately. 

Now,  since  the  final  volume  of  the  reaction  products  is 
approximately  92  +158  +4  =  254  at  a  temperature  of  100°  C., 
while  after  removal  of  the  steam  it  falls  to  92  +  4  =  96,  the 
pressure  of  carbon  monoxide  in  the  cooled  gas  after  removal 
of  the  carbon  dioxide,  will  be — 

0*093  X  254 
— ^ — ^-±  =  0*25  mm. 
96 

or  0*032  %. 

The  hydrogen  produced  commercially  by  this  process 
is  stated  to  have  the  following  percentage  composition  : — 

Hydrogen    ..  97*5 

Carbon  monoxide  . .          . .  0*0-0*2 

Methane 0*3-0*5 

Nitrogen      . .          . .         . .  1*5-2*0 

The  cost  of  production  depends  on  the  size  of  the  instal- 
lation, but  for  moderate  plants  in  continuous  operation  the 
cost  is  stated  to  be  2/2^-2/9  per  1000  ft.3  (pre-war),  while 
for  large  plants  it  falls  to  1/8  (I/epsius,  Monit.  Sclent.,  (1912), 
493).  As  the  reaction  is  exothermic  it  is  only  necessary  to 
supply  heat  at  the  commencement  of  the  operation.  The  lime 


168  INDUSTRIAL  GASES 

container  requires  to  be  cooled  and  the  waste  heat  may  be 
utilized  for  the  generation  of  the  steam  for  the  process.  One 
advantage  claimed  is  the  comparatively  low  temperature  at 
which  the  operation  is  conducted  as  compared  with  the 
I/ane  and  allied  processes,  for  instance,  repairs  being  thus 
minimized. 

The  process  does  not  appear  to  have  been  used  on  any 
considerable  scale — the  handling  of  the  large  amounts  of 
lime  presents  some  difficulty. 

MANUFACTURE  FROM  WATER  GAS  BY  LIQUEFACTION 
OF  THE  CARBON  MONOXIDE 

This  purely  physical  method  of  separating  hydrogen  from 
water  gas  is  in  use  on  a  fairly  extensive  scale  and  was  the 
process  installed  by  the  Badische  Co.  in  their  first  synthetic 
ammonia  factory.  It  depends  on  the  approximate  separation 
of  the  carbon  monoxide  and  nitrogen  as  liquid  by  cooling 
under  pressure  to  about  —200°  C.  The  general  trend  of  the 
process  may  be  seen  from  the  following  table  :— 

Gas  . .          . .          . .     Vapour  pressure  of  liquid  at 

-200°  C. 

Hydrogen    . .          . .     (Above  critical  temperature, 

namely  — 241-2°  C.) 
Carbon  monoxide  . .     0-57  atm. 
Nitrogen      . .          . .     0*33  atm. 

A  brief  resume  will  first  be  given  of  the  principal  patents 
relating  to  this  process. 

Parkinson,  in  B.P.  4411/92,  deals  with  the  separation  of 
the  constituents  of  gases  such  as  air  and  water  gas  by  frac- 
tionation,  etc.  Some  of  the  other  early  patents  relating  to 
the  liquefaction  of  the  permanent  gases  have  a  bearing  on  the 
separation  of  hydrogen  from  other  gases,  but  the  most  im- 
portant are  those  given  below.  According  to  B.P.  7205/11, 
of  the  Gesellschaft  fur  Linde's  Eismaschinen,  A.G.,  the 
compressed  hydrogen-carbon  monoxide  mixture  is  cooled 
by  passing  through  a  heat-interchanger,  the  cooling  effect 
of  which  may  be  augmented  by  means  of  liquid  air  or  nitrogen. 


HYDROGEN 


169 


Partial  liquefaction  takes  place  under  pressure  'and  the  two 

phases  are  then  allowed  to  expand  in  separate  streams  into 

the    above    mentioned 

heat  -  interchanger     in 

counter-current  to  the  «•— 

incoming      gas.      The 

hydrogen,    before    ex^ 

pansion,  however,  may 

pass  through  a  second 

heat  -  interchanger     in 

counter-current  to  the 

expanded       hydrogen, 

whereby   more   carbon 

monoxide  is  deposited 

in  a  chamber  connected 

to  the  first  liquefaction 

chamber,  the  hydrogen 

being    thus     rendered 

purer, 

A  subsequent  patent, 
B.P.  9260/11,  deals 
with  certain  modifica- 
tions :  (i)  a  more 
thorough  fractionation 
is  effected  by  cooling 
either  the  mixed  in- 
coming gases  or  the 
hydrogen  fraction  (as 
in  Fig.  1 6)  before  its 
expansion,  with  liquid 
air  or  nitrogen  boiling 
under  reduced  pressure, 
a  lower  temperature 
being  thus  secured  :  (2) 
the  hydrogen  may  be 
expanded  either  with  or  without  the  performance  of  external 
work,  in  the  former  case  the  hydrogen  may  be  slightly 
heated  by  the  incoming  gases  before  they  are  cooled  by  the 


FIG.  1 6. — Linde's  system  for  the  separa- 
tion of  hydrogen  from  water  gas  by  lique- 
faction of  the  carbon  monoxide. 


170  INDUSTRIAL   GASES 

evaporation  of  the  liquid  carbon  monoxide  fraction,  in  order 
to  prevent  blocking  up  by  solidification  on  expansion ;  the 
cooling  effect  of  the  external  work  may  be  used  to  cool  the 
hydrogen  leaving  the  chamber  in  which  separation  of  the 
carbon  monoxide  has  taken  place,  further  carbon  monoxide 
being  deposited  :  (3)  the  hydrogen  may  be  led  away  in  the 
compressed  state,  the  extra  cooling  necessary  being  supplied 
by  the  liquid  air  boiling  under  reduced  pressure. 

A  simplified  apparatus,  described  by  the  Maschinenbau- 
Anstalt-Humboldt  in  F.P.  445883/12,  differs  from  the  above 
in  that  the  compressed  water  gas,  after  traversing  a  heat- 
interchanger,  passes  through  a  coil  immersed  in  evaporating 
carbon  monoxide  and  then  expands  into  a  chamber  where 
carbon  monoxide  is  deposited.  The  hydrogen  escapes 
directly  through  the  heat-interchanger,  while  the  carbon 
monoxide  is  siphoned  off  to  the  above  mentioned  evapora- 
tion chamber  and  after  vaporizing  enters  the  heat-inter- 
changer.  B.P.  7147/13  of  the  Soc.  1'Air  lyiquide  deals  with  a 
combination  of  the  liquefaction  process  with  the  Griesheim- 
Elektron  process  (cf.  p.  164)  whereby  the  production  of 
hydrogen  per  volume  water  gas  is  increased.  The  carbon 
monoxide-rich  portion,  after  vaporization,  is  passed  over 
heated  slaked  lime  and  the  resulting  gas,  mainly  hydrogen, 
added  to  the  water  gas  entering  the  liquefaction  system. 
An  attempt  is  made  by  the  Badische  Co., in  D.R.P.  285703/13, 
to  avoid  the  necessity  for  supplementary  cooling  by  liquid 
air,  by  the  addition  of  excess  of  carbon  monoxide  or  nitrogen, 
both  of  which  gases  show  a  positive  Joule-Thomson  effect. 
This  may  be  accomplished  by  returning  the  more  volatile 
portion  of  the  carbon  monoxide  fraction,  containing  hydrogen, 
to  the  water  gas*supply. 

In  B.P.  13160/14,  Claude  (Soc.  1'Air  I^iquide)  describes 
apparatus  some  what  similar  to  that  of  I^inde.  The  compressed 
water  gas  is  divided  into  two  portions  which  are  cooled  by 
passing  through  two  independent  auxiliary  heat-interchangers 
AA  (Fig.  17),  traversed  respectively  by  counter-currents  of 
the  expanded  hydrogen  and  carbon  monoxide.  After  re- 
union of  the  two  streams  of  water  gas,  the  carbon  monoxide 


HYDROGEN 


171 


fraction  is  deposited  in  a  separation  chamber  B*,  the  liquid 
and  gaseous  phases  being  then  treated  separately  in  the  two 
portions,  B  and  C  (Fig.  18)  of  the  heat-interchanger  situated 
above  B1  ;  the  hydrogen  passes  through  both  sections  in 
vertical  tubes.  The  lower  part  B  contains,  under  atmospheric 
pressure,  liquid  carbon  monoxide  which  is  fed  in  from  the 
separating  chamber  B1..  The  liquid  carbon  monoxide  passes 


FIG.  17. — Claude  fractionation  system. 

(1)  through  a  coil  S  immersed  in  the  liquid  contained  in  the 
lower  part  of  the  heat-interchanger  B,  being  cooled  thereby  ; 

(2)  through  a  coil  S1  immersed  in  a  small  interchanger  filled 
with  the  liquid  released  to  atmospheric  pressure  from  the 
same  coil  S1,  and  (3)  after  this  release  of  pressure  into  a  tank 
E  surrounding  the  hydrogen  tubes  in  the  upper  part  of 
section  B  of  the  interchanger,  finally  overflowing  into  the 
main  bulk  of  liquid  carbon  monoxide  below.     The  object 
of  this  rather  complicated  procedure  is  to  utilize  the  lower 


172 


INDUSTRIAL   GASES 


temperature  of  the  carbon  monoxide  deposited  in  B1  (in 
which  carbon  monoxide  some  hydrogen  is  retained  on 
account  of  its  separation  under  pressure)  to  further  cool  the 
hydrogen  and  so  cause  more  complete  deposition  of  the 
carbon  monoxide  therefrom.  With  this  method  of  working, 
the  hydrogen  passes  through  tubes  cooled  by  (i)  liquid 

carbon  monoxide  evaporating 
under  atmospheric  pressure  ; 
(2)  liquid  carbon  monoxide 
containing  some  hydrogen  also 
evaporating  under  atmospheric 
pressure ;  and  (3)  the  gases  in 
the  upper  part  C  of  the  inter- 
changer.  Here  the  hydrogen 
is  still  further  cooled  by  passing 
to  an  engine  D  in  which  expan- 
sion takes  place,  the  expanded 
gases  being  led  back  to  the 
interchanger.  The  carbon 
monoxide  deposited  in  the 
tubes  falls  back  to  the  separa- 
tion chamber  B1.  If  desired 
the  cooling  effect  may  be  in- 
creased by  the  expansion  of 
supplementary  compressed  hy- 
drogen. If  high  purity  of  the  hydrogen  is  unnecessary, 
the  simpler  type  of  separator  shown  in  Fig.  17  may  be 
employed. 

The  Linde-Frank-Caro  Process 

Several  L,inde-Frank-Caro  plants  have  been  installed  on 
the  Continent  and  one,  of  about  17,000  ft.3  per  hour  capacity, 
by  Messrs.  Ardol,  L,td.,  in  this  country. 

Water  gas,  which  contains  about  50  %  hydrogen,  the 
residue  being  mainly  carbon  monoxide  with  smaller  quan- 
tities of  carbon  dioxide,  nitrogen  and  methane,  passes  through 
a  scrubber  to  a  holder  and  is  then  compressed  to  about 
25-50  atmospheres.  Under  this  pressure  it  is  freed  from 


FIG.  18.- 


-Claude  fractionation 
system. 


HYDROGEN  173 

carbon  dioxide   by  washing   with   water — Bedford   process 
(cf.  also  B.A.M.A.G.  process,  p.  161) — and  subsequently  with 
caustic  soda.     After  being  dried  by  refrigeration  with  an 
ammonia  or  carbon  dioxide  plant,  the  compressed  gas  enters 
the   separator.     Passing  first  through   a  heat-interchanger 
in  counter-current  to  all  the  outgoing  gases,  the  compressed 
gas  traverses  a  coil  immersed  in  liquid  carbon  monoxide 
boiling  under  atmospheric  pressure.     Here  the  greater  part 
of  the  carbon  monoxide  is  condensed  and  a  little  of  the 
nitrogen.     The  liquid  and  gaseous  phases  are  separated  in 
a  special  vessel  and  the  hydrogen,   still  containing  some 
5-6  %  carbon  monoxide  and  nitrogen,  passes  on  to  a  tube 
system  cooled  to  about  —200°  C.  by  means  of  liquid  air  or 
nitrogen  boiling  under  reduced  pressure.     The  liquid  carbon 
monoxide  and  nitrogen  separated  at  this  stage  flow  back  to 
the  main  portion  in  the  separation  vessel  from  which  the 
liquid  passes  through  a  valve  to  the  vessel  containing  liquid 
carbon  monoxide  at  atmospheric  pressure,  used  to  cool  the 
compressed  gases  as  mentioned  above.     By  means  of  careful 
lagging  the  heat  losses  are  made  very  small  so  that   only 
relatively  little  liquid  nitrogen  is  needed.      The   hydrogen 
leaves  the  apparatus  through  the  heat-interchanger  under 
the  same  pressure  as  that  of  entry,  consequently  little,  if  any, 
energy  is  required  for  its  subsequent  utilization  for  the  manu- 
facture of  synthetic  ammonia,  the  hydrogenation  of  oils,  etc. 
The  arrangement  is  identical  with  that  represented  dia- 
grammatically  in  Fig.  16  except  that  the  hydrogen  is  carried 
back  through  the  interchanger  without  release  of  pressure. 
After  evaporation,  the  carbon  monoxide  fraction,  which  has 
a  purity  of  80-85  %>  corresponding  to  a  loss  of  about  15  % 
of  the  hydrogen,  passes  to  a  gas  engine,  the  power  generated 
being  sufficient  to  drive  the  whole  plant.     The  hydrogen 
fraction  has  obviously  a  very  high  degree  of  purity  as  regards 
sulphur   and  phosphorus  compounds,  heavy  hydrocarbons, 
etc.,  and  the  following  percentage  composition  is  claimed  :— 
Hydrogen     ..          ..          ..     97-97-5 

Carbon  monoxide   . .          . .         2-1 '7 

Nitrogen       i-0'8 


174  INDUSTRIAL  GASES 

The  volume  of  hydrogen  is  about  40  %  of  the  original 
water  gas.  This  purity  is  sufficient  for  many  purposes,  but, 
if  desired,  further  purification  may  be  effected,  see  p.  207. 

On  account  of  the  fractionation  of  the  liquid  air  which 
may  be  produced  in  the  separator  itself,  or  in  very  large 
plants  in  a  separate  apparatus,  nitrogen  and  oxygen  may  be 
obtained  as  by-products.  The  operations  may  be  so  regu- 
lated that  the  former  is  produced  in  the  proportion  required 
for  combination  with  the  hydrogen  to  form  ammonia. 

The  following  particulars  are  given  by  Sander  (Z.  angew. 
Chem.,  (1912),  2401)  for  different  sizes  of  plants  : — 

TABLE  22. 
LINDE- FRANK  CARO  HYDROGEN  PLANTS. 


Hourly  output  (ft.8  of  hydrogen) 

880          3500 

17,700 

Water  gas  used  per  hour  (ft.3) 

2500          8800 

44,000 

Coke  used  per  hour  (Ibs.) 

no            350 

1700 

Cooling  water  used  per  hour  (gallons)   .  . 

500           1700 

7000 

Plants  producing  3500  and  35,000  ft.3  of  hydrogen  per 
hour  are  stated  to  cost  about £13,000  and £80,000  respectively, 
while  the  cost  of  production  of  the  hydrogen  by  this  process 
is  claimed  to  be  about  3/-  to  4/-  per  1000  ft.3  for  medium- 
sized  plants  (all  on  pre-war  basis).  The  labour  required  in 
working  the  plant  is  small  on  account  of  the  continuous 
nature  of  the  operations.  One  advantage  of  the  process  when 
used  in  connection  with  the  hydrogenation  of  oils  is  the  ease 
with  which  the  residual  impure  hydrogen  may  be  purified 
again.  On  the  other  hand  repairs  are  somewhat  heavy. 

MANUFACTURE  BY  THE  ACTION  OF  WATER  OR  STEAM  ON 
IRON  OR  CARBON 

General. — The  processes  falling  under  this  heading  are 
all  capable  of  representation  by  the  following  equation  : — 

H20  +  R  =  H2  +  RO 

Generally  speaking,  R  may  be  any  substance,  usually 
an  element,  which  has  the  power  of  uniting  with  oxygen, 


HYDROGEN 


175 


but  in  practice  only  iron  and  carbon  find  application  for  this 
purpose  leaving  out  of  consideration  certain  methods  used  for 
field  purposes,  e.g.  the  action  on  water  of  sodium  or  other 
active  elements. 


Iron  Oxide  Processes.    The  Alternate  Action  of  Steam 
and  Reducing  Gases  on  Heated  Iron 

At  a  red  heat  iron  reacts  with  steam  according  to  the 
following  equation  :  — 


4H20  +  3Fe  =  4H2  +  Fe3O4 

The  action  is  reversible  and  the  ratio  of  pnzo/Pnz  f°r 
different  temperatures  is  given  below,  the  equilibrium 
relations  for  the  two  stages  of  the  reaction  being  separated 
(Chaudron,  Comptes  Rend.,  159,  (1914),  237).  The  values 
are  taken  from  a  smoothed  curve. 

SYSTEM  Fe/FeO/H2/H2O. 


Temperature  °C.  .  . 

4OO 

5OO 

6OO 

700 

800 

850 

PR20/P&2 

0-15 

0-23 

°'33 

0-46 

0-61 

0*70 

SYSTEM  FeO/Fe3O4/H2/H2O. 


Temperature  °C.  .  .         400 
£H  o/PH      •  •           ••        °'2o 

500 
0-32 

600 
0-52 

700 
0-85 

800           850 

cf.  also  Wohler  and  Prager,  Z.  Elektrochem.,  23,  (1917), 
199. 

It  is  evident  that  reduction  is  favoured  by  increase  of 
temperature.  On  passing  a  continuous  current  of  steam  or 
hydrogen  over  the  iron  or  iron  oxide  heated  to  redness,  the 
reaction  proceeds  to  completion  giving  oxide  or  metal 
respectively. 

This  method  of  making  hydrogen  has  long  been  recog- 
nized and  we  find  patents  dealing  with  the  alternate  action 
of  steam  and  reducing  gases  on  iron  as  early  as  1861  (Jacob, 
B.P.  593/61  •'  cf-  also  Baggs,  B.P.s  2719/65  and  1471/73), 


176  INDUSTRIAL   GASES 

One  of  the  first  attempts  at  technical  production  by  this 
method  appears  to  have  been  made  by  Giffard  in  1878,  who 
employed  a  shaft  filled  with  ore.  Water  gas  was  used  with- 
out purification  and  for  this  reason,  coupled  with  the  irregular 
temperature  distribution  in  the  shaft  type  of  plant,  the  life 
of  the  ore  was  very  short. 

The  first  patent  of  commercial  importance  is  that  of 
Lewes,  B.P.  20752/90,  according  to  which  a  retort  containing 
iron  turnings  or  moulded  oxide,  etc.,  is  heated  to  bright 
redness  by  imbedding  in  a  producer,  the  air  producer  gas  from 
which  is  used  in  the  reduction  phase,  the  metal  being  then 
treated  with  steam.  This  procedure  would  obviously  give 
rise  to  over-heating  of  the  iron  oxide.  In  a  later  patent,  B.P. 
4134/91,  the  iron  oxide  is  disposed  on  pumice  or  mixed -with 
asbestos,  and  semi-water  gas  is  used  for  the  reduction.  A 
number  of  patents  dealing  with  special  forms  of  plant  follow. 
An  important  point  is  touched  on  by  the  Dellwik-Fleischer 
Wassergas  G.m.b.H.,  in  B.P.  21479/08,  which  prescribes  the 
addition  of  steam  to  the  reducing  gases  to  prevent  the 
deposition  of  carbon  ;  the  reduction  is  arrested  when  only 
half  the  oxide  is  reduced.  Burnt  pyrites  is  used  as  reaction 
material.  In  B.P.  17591/09,  I,ane  describes  an  arrangement 
of  valves  whereby  more  retorts  may  be  reduced  than  oxidized 
at  the  same  time,  this  being  desirable  by  reason  of  the  greater 
reaction  velocity  in  the  oxidation  phase.  The  first  portion 
of  the  hydrogen  is  diverted.  Impurities,  e,g.  sulphur,  are 
removed  by  occasionally  burning  out  with  air,  and  in  a  later 
patent,  B.P.  11878/10,  a  method  of  purification  of  the  gases 
from  carbon  dioxide,  sulphuretted  hydrogen,  and  sulphur 
dioxide,  by  washing  under  pressure  is  described.  Proposals 
have  been  made  to  use  molten  iron,  e.g.  as  in  B.P.  23418/10 
by  Gerhartz.  The  use  of  roasted  spathic  iron  ore  as  re- 
action material  is  claimed  by  Dieffenbach  and  Moldenhauer 
in  D.R.P.  232347/10,  while  B.P.  6683/12  of  the  Badische 
Co.  relates  to  the  prevention  of  loss  of  activity  through 
fusion  of  the  surface  of  the  iron,  by  using  iron  oxide  which 
has  been  melted  in  oxygen  ;  refractory  oxides  may  be  added. 
Dieffenbach  and  Moldenhauer  in  a  further  patent,  B.P. 


HYDROGEN  177 

12051/12,  propose  to  prevent  deterioration  by  the  use  of 
alloys  of  iron  with  manganese,  tungsten,  titanium,  etc. 
Mixtures  of  nitrogen  and  hydrogen  may  be  obtained  by 
passing  air  and  steam  over  the  iron,  or,  alternatively,  pure 
nitrogen  may  be  obtained  by  using  air  alone. 

Among  various  patents  describing  means  of  avoiding  fall 
in  output  may  be  mentioned  B.P.  12117/12  by  Messerschmitt, 
according  to  whom  the  effects  of  fusion  of  the  iron  oxide 
in  producing  obstruction  are  avoided  by  the  use  of  a  skeleton 
of  compact  iron,  and  B.P.  27735/12  (Badische  Co.),  where  loss 
of  activity  is  prevented  by  the  use  of  spongy  iron  obtained  by 
imbedding  Swedish  iron  ore  in  carbon  and  heating  from  the 
outside.  We  come  next  to  a  series  of  patents  by  Messer- 
schmitt. B.P.s  12242/12  and  12243/12  deal  with  special 
methods  of  construction  of  plant,  the  latter  describing  the 
annular  type  of  ore  container  detailed  later.  According  to 
B.P.  17690/13,  the  reduction  of  the  oxide  is  effected  by  gases 
of  high  calorific  power  and  the  heating  by  gases  of  low  calorific 
power,  e.g.  the  spent  reducing  gases,  fusion  being  thus 
avoided,  while  B.P.  17691/13  advocates  the  reduction  of 
the  charge  by  means  of  a  partly  burnt  mixture  of  gas  with 
air  in  insufficient  quantity  for  complete  combustion.  Modifi- 
cations in  construction  are  prescribed  in  B.P.s  17692/13, 
in  18942/13  and  in  D.R.P.  291902/14.  B.P.  18028/13  is 
concerned  with  the  use  of  iron-manganese  ores  in  order  that 
lower  temperatures  may  be  employed,  thus  avoiding  absorption 
of  carbon,  sulphur,  etc.  According  to  D.R.P.  291603/13,  the 
iron  is  oxidized  to  the  stage  of  ferrous  oxide,  giving  hydrogen, 
and  then  further  with  air,  giving  nitrogen.  Among  numer- 
ous other  patents  may  be  mentioned  B.P.  16893/14  by 
Dempster,  according  to  whom  leakage  of  gas  from  one  part 
of  the  system  to  another  is  prevented  by  suitable  water 
seals,  and  B.P.  12698/15  by  Maxted  and  Ridsdale,  where  the 
deposition  of  carbon  or  the  formation  of  carbide  from  the 
gases  in  the  reducing  phase  is  prevented  by  the  presence 
of  carbon  dioxide  to  the  extent  of  at  least  twice  the  volume 
of  the  carbon  monoxide  ;  contamination  of  the  hydrogen 
in  the  subsequent  treatment  with  steam  is  thus  avoided. 

A.  12 


178  INDUSTRIAL  GASES 

This  procedure  is  equivalent,  of  course,  to  the  addition 
of  steam  as  set  forth  in  B.P.  21479/08,  see  p.  176. 
In  B.P.  119591/18,  Thorssell  and  L,unden  propose  to  in- 
crease the  active  life  of  the  reaction  material  by  impreg- 
nating iron  sponge  with  a  solution  of  alkali  hydrate  or 
carbonate. 

Of  the  modifications  of  this  method  of  producing  hydro- 
gen which  are  now  in  extensive  use  may  be  mentioned  the 
lyane,  the  Messerschmitt  and  the  Internationale  Wasserstoff 
A.  G.  (B.A.M.A.G.)  processes. 

Lane  Process. — This  process,  or  as  modified  by  Dempster, 
Messrs.  Humphrey  and  Glasgow  and  others,  is  the  one  most 
commonly  adopted  in  this  country  for  the  production  of 
hydrogen  on  a  large  scale.  Calcined  spathic  iron  ore, 
disposed  in  vertical  cast-iron  retorts,  is  alternately  reduced 
by  water  gas  and  oxidized  by  steam. 

From  the  equations 

Fe3O4  +  2CO  +2H2  =  sFe  +  2CO2  +  2H2Ogas  -  18,000 

calories 
3Fe  +  4H2Ogas  =  Fe3O4  +  4H2  +  38,400  calories 

it  will  be  seen  that  the  reduction  is  endothermic  while  the 
oxidation  is  exothermic.  As  regards  the  reduction  by  a 
mixture  of  carbon  monoxide  and  hydrogen,  the  interaction 
of  the  latter  reducing  agent  absorbs  a  large  amount  of  heat, 
while  that  of  the  former  is  very  slightly  exothermic  ;  on 
this  basis  Jaubert  effects  economy  in  the  fuel  required 
for  maintaining  the  reaction  temperature  by  working  at  a 
lower  temperature  so  that  the  carbon  monoxide  acts 
preferentially.  This  method  of  procedure  (L^ane- Jaubert 
process)  has  probably  corresponding  disadvantages  in  in- 
creasing the  deposition  of  carbon  in  the  reducing  phase 
and  consequently  raising  the  carbon  monoxide  content  of 
the  hydrogen  (see  below). 

The  ore  is  contained  in  vertical  cast-iron  retorts  about 
9  inches  internal  diameter  and  nearly  10  ft.  long,  a  plant 
generating  3500  ft.3/hr.  having  36  such  retorts,  arranged  in 
three  groups  each  of  12  retorts  (Fig.  19).  Since  the  total 


HYDROGEN  179 

internal  volume  of  such  a  set  equals  159  ft.3  the  "  space- 


velocity"  is  ft.  3  hydrogen/ft.3/hr.  =22  ft.3  hydrogen/ 

ft.3/hr.     The  ends  of  the  retorts  are  flanged  and  closed  by 


Front       Elevation 


FIG.  19. — Lane  Hydrogen  Plant  (The  Engineer). 

plates  with  asbestos  joints.  Heating  of  the  retorts  to 
650-700°  C.  is  effected  either  by  means  of  a  built-in  producer 
or  by  the  combustion  of  water  gas  which,  of  course,  needs  no 
purification. 

The  method  of  operation  is  as  follows  : — Two  of  the  three 


i8o 


INDUSTRIAL   GASES 


groups  are  supplied  with  water  gas  for  20  minutes,  whereby 
reduction  of  the  oxide  takes  place,  and  then  treated  with 
steam  for  10  minutes,  the  reduction  occupying  more  time 
than  the  oxidation.  During  the  reduction  phase  the  carbon 
monoxide  and  hydrogen  of  the  water  gas  are  only  partty 
utilized  and,  consequently,  the  exit  gases  are  used  for  heating 
the  retorts,  first  passing  through  a  condenser  to  remove  the 


To     1  Atmosphere 


Hydrogen 


FIG.  20. — Diagram  of  the  Lane  Hydrogen  Retort  Furnace 
(The  Engineer}. 

steam.  When  reduction  is  complete,  the  retorts  contain 
water  gas  which,  if  passed  into  the  hydrogen  gas-holder, 
would  introduce  carbon  monoxide  ;  for  this  reason  "  scav- 
enging "  is  resorted  to,  i.e.  for  a  short  time  after  admitting 
steam,  the  impure  hydrogen  is  passed  back  into  the  water 
gas  main  and  is  thus  not  lost.  Connection  is  then  made  to 
the  hydrogen  main.  A  convenient  arrangement  of  change- 
over valves,  as  shown  diagrammatically  in  Fig.  20,  is  employed 
to  effect  these  operations.  When  changing  from  the  oxidizing 
to  the  reducing  phase  the  valve  H  is  operated  slightly  in 


HYDROGEN  181 

advance  of  the  valve  K.  The  spent  reducing*  gases,  still 
containing  some  combustible  gases,  on  leaving  the  retorts 
pass  to  condensers  in  which  the  bulk  of  the  steam  formed  in 
the  retorts  is  separated,  and  then  are  led  to  the  combustion 
chamber. 

It  is  important  carefully  to  purify  the  water  gas  used  in 
the  reduction  of  the  ore,  as  sulphur  compounds  exert  a  dele- 
terious influence  causing  disintegration  and  loss  of  activity. 
The  water  gas  passes  from  the  generators  through  a  heat- 
interchanger  in  counter-current  to  the  steam  entering  the 
generator,  through  a  water  scrubber  to  a  gas-holder  from  which 
it  is  drawn  by  an  exhauster  into  a  series  of  purifiers  charged 
with  bog  iron  ore  to  remove  sulphur  compounds,  and  then 
enters  the  retorts.  Four  purifiers  form  a  set,  three  being 
in  use  at  once,  the  gas  passing  the  three  in  series,  entering 
the  foulest  first.  The  thorough  elimination  of  the  sulphur- 
etted hydrogen  from  the  water  gas  has  an  important  bearing 
on  the  life  of  the  reaction  material. 

During  the  reduction  phase  there  is  some  deposition  of 
carbon  arising  from  decomposition  of  carbon  monoxide. 

2CO  =  CO2  +  C  +  39,300  calories  (cf.  p.  237). 

(For  a  fuller  study  of  the  complex  equilibria  of  the 
system  Fe/FeO/Fe3O4/CO/CO2/C,  reference  should  be  made 
to  Baur  and  Glassner,  Z.  physik.  Chem.,  43,  (1903),  354 ; 
cf.  also  Carpenter  and  Smith,  Trans.  Iron  and  Steel  Inst., 
September,  1918.) 

On  passing  steam,  this  carbon  gives  rise  to  carbon 
monoxide  and  carbon  dioxide  in  the  hydrogen.  To  minimize 
this  effect  and  to  remove  accumulations  of  sulphur  com- 
pounds, the  retorts  are  periodically  "  burnt  out  "  by  blowing 
air  through  them. 

Many  attempts  have  been  made,  as  has  been  mentioned 
in  the  patent  synopsis,  to  prevent  the  deposition  of  carbon 
in  the  reducing  phase.  Thus,  Maxted,  of  Gas  Developments, 
I/td.,  proposes  to  introduce  sufficient  carbon  dioxide  into  the 
reducing  gases  to  give  a  CO2/CO  ratio  higher  than  that 
corresponding  to  the  CO2/CO/C  equilibrium  (cf.  p.  237)  by 


182  INDUSTRIAL  GASES 

using  instead  of  ordinary  water  gas,  a  "  converted  "  water 
gas  (B.P.  12698/15;  B.P.  125112/16,  see  p.  177).  It  should 
be  pointed  out  that  the  equilibrium  ratio  of  CO2/CO  is  not 
that  given  on  pp.  238-9  for  any  particular  temperature,  e.g. 
700°  C.,  but  varies  with  the  actual  joint  partial  pressure  of 
carbon  monoxide  and  carbon  dioxide.  By  working  from  the 
value  of  Kt,  which  equals  pcoJP2co>  it  is,  however,  easy  to 
calculate  the  ratio  for  any  particular  condition. 

On  leaving  the  retorts  the  hydrogen  passes  through  a 
scrubber,  then  through  lime  purifiers,  where  carbon  dioxide, 
resulting  from  the  oxidation  of  carbon  monoxide  in  accordance 
with  the  water  gas  equilibrium,  is  removed,  into  a  holder. 

The  temperature  of  the  retorts  is  a  matter  of  considerable 
importance,  on  account  of  its  bearing  on  carbon  deposition 
on  the  one  hand,  and  on  the  life  of  the  retorts  on  the  other. 
The  usual  practice  is  to  employ  a  temperature  of  about 
650°  C.  The  retorts  are  stated  to  last  about  12  to  1 8  months 
and  the  ore  about  6  months.  Assuming  the  life  of  the  retorts 
to  be  12  months,  the  depreciation  is  equivalent  to  a  charge 
of  about  $d.  per  1000  ft.3  of  hydrogen. 

In  good  practice,  2-3  volumes  of  water  gas  are  necessary 
for  each  volume  of  hydrogen  produced. 

A  considerable  number  of  plants  have  been  erected  in 
this  country,  in  France  and  in  Russia.  The  purity  of  the 
hydrogen  may  be  fairly  high  with  careful  working,  e.g. 
99'5~99'75  %>  the  main  impurities  being  carbon  monoxide 
and  a  little  (e.g.  0-25  %)  nitrogen.  Plants  are  made  with 
capacities  from  250-10,000  ft.3/hr.  The  cost  of  the 
hydrogen  produced  by  this  method  is  of  the  order  of  3/-  to 
4/-  per  1000  ft.3  plus  overhead  charges  (pre-war). 

The  Messerschmitt  Process. — This  process  has  come 
into  considerable  use  in  Germany  and  was  largely  adopted 
by  the  German  War  Department,  which  had  some  fifteen 
plants  of  3500-20,000  ft.3/hr.  capacity  (Barnitz,  Met.  and 
Chem.  Eng.,  15,  (1916),  494  ;  /.  Soc.  Chem.  Ind.,  (1916), 
1136). 

It  differs  from  the  I^ane  process  in  having  much  larger 
units  which  are  of  annular  form  in  order  to  minimize 


HYDROGEN 


183 


variation  of  temperature.  The  latest  type  consists  of  an 
upright  cylindrical  shaft  lined  with  firebrick  into  which  shaft 
two  concentric  iron  cylinders  are  built  (Fig.  21).  Of 
these,  the  inner  one  rests  on  the  floor  of  the  generator  while 


FIG.  21. — Messerschmitt  Hydrogen  System. 

the  other  is  raised  slightly  to  afford  room  for  the  admission 
of  the  gases.  The  reaction  material  (iron  ore  or  iron- 
manganese  ore)  is  disposed  in  the  annular  space  between  the 
two  cylinders.  Chequer-work  in  the  inner  cylinder  and 
between  the  outer  cylinder  and  the  furnace  wall,  serves  to 
retain  and  regenerate  the  heat.  A  mixture  of  water  gas 


184  INDUSTRIAL  GASES 

with  insufficient  air  for  complete  combustion  is  burnt  in  the 
inner  cylinder  and  the  products  of  incomplete  combustion 
pass  downwards  through  the  reaction  mass  in  the  annulus 
and  upwards  again  outside  the  outer  cylinder  (secondary 
air  being  added  at  the  last  stage)  and  so  out  to  the  flue. 
After  some  20  minutes,  during  which  a  temperature  of 
700-800°  C.  is  maintained,  the  water  gas  and  air  are  cut 
off  and  steam  is  passed  into  the  generator  from  below.  The 
issuing  impure  gases  are  allowed  to  escape  for  a  few  seconds 
into  the  flue  ;  at  this  point  the  steam  is  diverted  so  as  to 
enter  at  the  top  of  the  outer  chamber,  passing  up  through 
the  reduced  iron,  the  hydrogen  being  taken  off  at  the  top. 
Ten  minutes  suffices  for  the  steaming  operation,  whereupon 
the  cycle  is  repeated.  The  course  of  the  combustion  in  the 
furnace  may  be  reversed  or  the  two  directions  may  be 
alternated.  In  the  Messerschmitt  process  the  effect  of  carry- 
ing out  the  reduction  with  the  partially  burnt  gases  from  the 
central  heating  chamber  should  be  to  prevent  or  minimize 
the  deposition  of  carbon  on  the  reaction  material  owing  to 
the  presence  of  carbon  dioxide  and  its  equivalent  for  this 
purpose,  steam.  The  hydrogen  is  subjected  to  a  final 
purification  as  in  the  I^ane  process. 

Among  the  advantages  claimed  for  the  system  are  the 
ease  of  control  of  the  working  temperature  and  the  avoid- 
ance of  overheating.  The  purity  of  the  gas  is  variously 
stated  to  be  98-5  to  99*2  %,  while  the  cost,  which  varies 
with  the  size  of  the  plant,  is  claimed  to  be  as  low  as  2/~-  per 
1000  ft.3  inclusive  of  capital  charges  (pre-war).  Little 
labour  is  demanded.  When  renewal  is  necessary  the  reaction 
mass  is  abstracted  through  Morton  doors  at  the  bottom. 
The  apparatus  is  easily  adapted  to  intermittent  working 
should  this  be  desired. 

Process  of  the  Internationale  Wasserstoff  A.G. — 
This  process  differs  little  in  principle  from  the  other  processes. 
In  its  earlier  form  the  plant  consisted  of  two  vertical  iron 
cylinders  heated  externally  to  700-800°  C.  The  process 
has  been  taken  over  recently  by  the  B.A.M.A.G.,  which  uses 
internally -heated  firebrick  shafts  ;  the  cycle  consists  of  three 


HYDROGEN  185 

periods,  namely,  heating,  reducing  and  steaming.  Water 
gas  of  the  highest  possible  calorific  power  is  used  for  the 
reduction,  the  excess  being  subsequently  burnt.  As  reaction 
mass,  large  lumps  of  burnt  pyrites  are  used.  Some  carbon 
is  deposited  from  the  gases ;  the  purity  of  the  hydrogen 
may  be  98-99  %  with  careful  working,  the  carbon  monoxide 
not  exceeding  0*8  %.,.  For  plants  producing  60,000  ft.3 
per  hour,  the  cost,  inclusive  of  labour  and  repairs,  is  stated 
to  be  about  3/4  per  1000  ft.3  (Sander,  /.  Gasbeleucht.,  58, 
(1915),  637)  (pre-war). 

Strache  Process. — An  older  process  due  to  Strache 
employs  three  vertical  iron  cylinders  set  in  firebrick,  of  which 
No.  i  is  a  water  gas  generator,  No.  2  contains  iron  oxide 
and  No.  3  is  a  regenerator.  The  steam  is  passed  in  the 
reverse  direction,  i.e.  from  3  to  i  via  2. 

With  reference  to  all  the  above  discontinuous  processes, 
the  general  statement  may  be  made  that  the  hydrogen  is 
liable  to  contain  variable  amounts  of  carbon  monoxide,  say 
O'25  to  i '5  %,  unless  subjected  to  further  purification. 

Dieffenbach   and  Moldenhauer  Process 

When  steam  is  passed  through  heated  carbon,  a  mixture 
of  carbon  monoxide,  carbon  dioxide  and  hydrogen  is  produced. 
In  usual  practice,  e.g.  in  making  water  gas,  the  operation 
is  conducted  so  as  to  give  a  high  CO/CO2  ratio ;  this  is 
effected  by  working  at  a  temperature  such  as  1000°  C. 
While  the  conversion  of  the  carbon  monoxide  of  water  gas 
into  carbon  dioxide  may  be  realized  by  the  B.A.M.A.G. 
process,  proposals  have  been  made,  especially  by  Dieffenbach 
and  Moldenhauer,  to  combine  the  two  stages  by  conducting 
the  actual  gasification  of  the  carbon  at  a  relatively  low 
temperature.  This  is  accomplished  by  impregnation  of  the 
coke  with  a  suitable  catalyst,  such  as  an  alkaline  salt,  to 
increase  the  reaction  velocity. 

The  idea  is  an  attractive  one  ;  on  the  other  hand,  there  is 
no  record  of  any  industrial  success  having  been  attained  by 
such  processes,  neither  are  technical  data  of  the  process 
available.  Such  a  process  is  unlikely  to  be  of  importance  in 


186  INDUSTRIAL  GASES 

the  production  of  pure  hydrogen  ;  the  matter  is,  however,  of 
sufficient  interest  to  warrant  a  brief  synopsis  of  the  main 
patents. 

According  toTessie  duMotay  andMarechal  (B.P.  2548/67) 
hydrogen  is  produced,  together  with  carbon  dioxide,  by 
heating  fuel  with  caustic  soda  or  lime.  B.P.  8426/92  by 
Krupp  is  similar.  Steam  is  passed  over  carbonaceous  matter 
mixed  with  hydrates,  carbonates,  etc.,  which  limit  the 
temperature  of  the  operation,  thus  reducing  the  percentage 
of  carbon  monoxide.  By  passing  over  red-hot  lime  the 
carbon  dioxide  is  removed  ;  this  lime,  as  also  that  used  in  the 
generating  retorts,  being  subsequently  regenerated  by  the 
passage  of  steam.  The  same  principle  is  elaborated  by 
Dieffenbach  and  Moldenhauer  in  B.P.  7718/10,  according  to 
which  carbon  is  impregnated  with  chlorides,  sulphates, 
sulphides,  etc.,  and  heated  with  steam  when  the  reaction 
takes  place  at  a  low  temperature,  e.g.  at  600°  C.,  producing 
only  a  little  carbon  monoxide.  Coal  may  be  impregnated 
and  then  coked  preparatory  to  being  heated  with  steam. 
The  operation  may  be  carried  out  in  externally-heated  retorts, 
or  oxygen  may  be  added  in  small  quantities  to  maintain  the 
temperature.  According  to  B.P.  7719/10,  charcoal  is  impreg- 
nated with  salts  especially  silicates,  and  treated  with  steam 
at  550-750°  C.  The  carbon  monoxide  content  of  the  hydro- 
gen is  claimed  not  to  exceed  a  few  tenths  per  cent.  In  B.P. 
7720/10  it  is  stated  that  better  results  are  obtained  by 
impregnating  crushed  coal  and  briquetting  the  product,  so 
counteracting  the  tendency  of  the  activity  to  fall  off  owing 
to  impregnation  being  only  local.  The  same  inventors,  in 
B.P.  8734/10,  advocate  the  addition  of  a  considerable  quantity 
of  lime  together  with  salts  in  order  to  take  up  the  carbon 
dioxide  and  lower  the  carbon  monoxide  content  (cf.  the 
Griesheim-Elektron  process).  For  example,  coke  is  first 
impregnated  with  10  %  potassium  carbonate  solution,  then 
mixed  with  5  times  its  weight  of  lime  and  heated  in  steam 
at  550-750°  C.  The  potassium  carbonate  limits  the  disso- 
ciation of  the  calcium  carbonate  by  making  the  reaction 
possible  at  a  lower  temperature. 


HYDROGEN  187 

Bergius  Process 

This  interesting  process  depends  on  the  action  of  liquid 
water  on  iron  or  carbon  at  temperatures  in  the  neighbourhood 
of  300°  C.,  and  consequently  under  pressures  at  least  equal 
to  the  vapour  pressure  of  water,  the  following  values  relating 
to  the  temperature  region  concerned  : — 

Temperature  °C.    •'*        . .     250  300  350 

Vapour  pressure  (atms.)  39  89  167 

Above  365°  C.,  i.e.  the  critical  temperature  of  water, 
no  liquid  can  be  present. 

If  carbon  is  used,  the  reaction  differs  from  that  obtaining 
in  a  gas  producer  in  that  the  conditions  for  carbon  monoxide 
production  are  much  less  favourable  at  the  lower  temper- 
ature in  question.  When  iron  is  employed,  the  low  temper- 
ature has  in  like  manner  the  effect  of  preventing  attack  by 
the  water  on  the  impurities  in  the  iron.  The  principal 
patents  relating  to  this  process  are  given  below. 

According  to  D.R.P.  259030/11  of  Bergius  and  Chemische 
Fabrik  vorm.  Moritz.  Milch  &  Co.,  carbon  is  heated  with  water 
under  high  pressure  to  about  300°  C.  In  an  example  cited, 
100  kilos,  coke,  200  kilos,  water,  and  i  kilo,  thallium  chloride 
are  heated  together  to  340°  C.  The  resulting  hydrogen  and 
carbon  dioxide  are  blown  off  at  intervals  and  the  carbon 
dioxide  absorbed  by  lime.  B.P.  19002/12  by  Bergius  relates 
to  the  use  of  iron ;  hydrogen  is  generated  by  the  action  of 
liquid  water  at  temperatures  above  100°  C.  on  iron  or  its 
lower  oxide,  preferably  in  the  presence  of  electrolytes,  e.g. 
ferrous  chloride.  Metallic  couples  may  be  formed  by  the 
presence  of  metals  electropositive  to  iron,  e.g.  an  iron- 
copper  couple  may  be  used.  In  one  example  iron  shavings 
are  treated  with  water  at  300°  C.,  the  pressure  being  kept 
at  150  atmospheres ;  while  in  another,  sodium  chloride  and 
a  plate  of  copper  are  added,  the  pressure  is  allowed  to  rise 
to  120  atmospheres  and  a  temperature  of  250°  C.  is  employed. 
In  an  addition  to  this  patent,  namely,  B.P.  19003/12,  Bergius 
describes  suitable  plant  for  carrying  out  the  operations. 
In  its  essentials  the  apparatus  consists  of  a  steel  pressure 


i88  INDUSTRIAL  GASES 

vessel  fitted  with  a  reflux  condenser,  dry  hydrogen  being  thus 
obtained.  D.R.P.  277501/13  describes  a  pressure  vessel 
containing  a  central  heating  tube  round  which  is  arranged 
a  series  of  reaction  tubes,  each  of  which  may  be  brought  in 
turn  under  a  feed  opening  in  the  cover  and  by  this  means 
frequent  removal  of  the  main  cover  is  avoided.  A  later 
patent,  D.R.P.  286961/13,  deals  with  the  use  of  water  in  the 
form  of  steam  at  temperatures  below  500°  C.  Electrolytes 
are  preferably  added  as  in  the  previous  patents. 

An  experimental  plant  was  erected  at  Hanover  (J.  Soc. 
Chem.  Ind.,  (1913),  462  ;  Z.  angew.  Chem.,  (1913),  i.,  517  ; 
Z.fiir  komp.  undflussige  Case,  (1915),  33)  to  test  the  Bergius 
process.  The  plant  consisted  of  six  vessels,  each  of  about 
i *6  ft.3  capacity  and  capable  of  generating  some  150  ft.3 
of  hydrogen  per  hour.  A  charge  of  iron  was  used,  contained 
in  a  vessel  inserted  from  the  bottom  of  the  bomb  and  forming 
a  lining  in  order  to  protect  the  bomb  itself  from  attack.  Some 
90  %  of  the  iron  was  oxidized  in  a  period  of  about  4  hours. 
With  carbon  the  action  was  rather  slow.  The  carbon  and 
sulphur  in  the  iron  are  stated  to  be  unattacked. 

In  the  following  table  are  to  be  found  comparative  rates 
of  reaction  as  influenced  by  additions  : — 


Reactanls. 

Temperature  °C. 

Hydrogen  generated  per  hour. 

Iron  4-  pure  water   .  . 
„     +FeCl2 
„     +  FeCl24-Cu.. 
„     +  FeCl2  +  Cu  .  . 

300 
300 
300 
340 

230  c.C. 
1390  c.c. 
1930  c.c. 
3450  c.c. 

On  leaving  the  reflux  condenser  with  which  each  bomb 
was  fitted,  the  hydrogen  passed  through  a  water  separator 
to  storage  cylinders.  The  gases  being  passed  through  a  spiral 
cooled  in  liquid  air  and  the  condensate  examined,  the  following 
analysis,  calculated  for  the  original  gas,  was  obtained  : — 

o/ 

/o 

Hydrogen      . .          . .          . .  99*95 

Carbon  monoxide     . .         . .       0*001 

Saturated  hydrocarbons     . .       0*04 
Unsaturated  hydrocarbons          o*oj 


HYDROGEN 


189 


By  passage  over  charcoal  at  liquid  air  temperatures,  a  purity 
of  99*995  %  could  be  obtained. 

This  process  has  certain  attractive  features — (i)  the  small 
floor  space  required  ;  (2)  its  suitability  for  small  plants, 
e.g.  for  field  work,  on  account  of  the  low  initial  cost  and 
the  discontinuous  nature  of  the  operations  ;  (3)  the  fact  that 
only  direct  fuel  heating  is  required  ;  (4)  the  production  of 
compressed  hydrogen  and  (5)  the  high  degree  of  purity 
of  the  hydrogen  produced.  One  would,  however,  expect 
repairs  to  be  rather  high  in  view  of  the  intermittent  character 
of  the  process  necessitating  very  frequent  breaking  of  large 
high  pressure  joints.  The  cost  of  hydrogen  produced  by  this 
method  is  stated  to  be  1/4 J  to  i/n  per  1000  ft.3  (pre-war). 


MANUFACTURE  OF  HYDROGEN  BY  THE  DECOMPOSITION 
OF  HYDROCARBONS 

Under  this  heading  may  be  described  a  number  of 
processes  all  of  which  depend  on  the  dissociation  of  hydro- 
carbons by  the  action  of  heat.  Such  dissociations  may  be 
attended  either  by  evolution  or  absorption  of  heat.  As  an 
example  of  the  first  class,  acetylene  is  typical — 

C2H2  =  2C  +  H2  +  47,800  calories. 

In  consequence  of  the  high  heat  evolution  accompanied 
by  no  change  in  volume,  the  equilibrium  conditions  give 
almost  complete  decomposition  except  at  very  high  temper- 
atures. With  exothermic  hydrocarbons  like  methane,  on 
the  other  hand,  the  degree  of  dissociation  rises  more  or  less 
rapidly  as  the  temperature  is  raised.  Thus,  taking  the  case 
of  methane,  we  have  the  following  equilibrium  conditions  at 
different  temperatures  for  the  equation  : — 

CH4  ^  C  +  2H2  —  21,700  calories, 


Temperature  °C.      .  . 

400 

500 

600 

700 

800 

900 

IOOO 

Percentage    of     me- 
thane in  the   dis- 

sociated product  .  . 

86-2 

62-5 

31-7 

in 

4'  4 

2 

I 

igo  INDUSTRIAL  GASES 

the  values  at  900°  and  1000°  C.  being  obtained  by  extrapo- 
lation. The  effect  of  temperature  on  the  equilibrium 
CH4  +H2O^CO  +  3H2  is  treated  on  p.  240. 

It  must  be  borne  in  mind  that  methane  is  a  very  stable 
vSubstance  and  that  the  equilibrium  values  are  only  slowly 
realized,  particularly  in  the  absence  of  catalysts,  until  temper- 
atures in  the  region  of  1000°  C.  are  attained.  Further,  the 
influence  of  increased  pressure  is  greatly  to  increase  the 
stability,  since  the  dissociation  constant  K  equals 


The  question  of  decomposing  hydrocarbons  has  long 
received  attention.  In  B.P.  1466/76,  St.  John  describes 
the  decomposition  of  coal  gas  hydrocarbons  by  passage 
through  incandescent  coke,  while  Stern,  in  B.P.  2787/80,  leads 
naphtha  vapour  with  steam  over  heated  lime.  Passing  over 
a  number  of  similar  patents  we  come  to  the  patents  of 
Rincker  and  Wolter,  F.P.s  391867/08  and  391868/08,  according 
to  which  two  coke-filled  generators  are  heated  to  incandes- 
cence by  the  injection  of  air  ;  tar,  oil,  or  other  suitable 
hydrocarbon  is  then  introduced  into  one  generator,  under- 
going transformation  into  hydrogen  and  carbon  which  is 
deposited  in  the  generator.  The  generators  are  used  alter- 
nately. A  new  line  is  taken  by  Machtolf  in  B.P.  14601/06. 
According  to  this  patent,  acetylene  compressed  to  4  to  6 
atmospheres  and  mixed  with  oil  gas,  etc.,  is  exploded  electri- 
cally ;  hydrogen  and  lampblack  are  thus  produced.  In 
B.P.  15071/09,  I^essing  describes  the  production  of  hydrogen 
from  coal  gas  by  passing  through  a  retort  either  empty  or 
containing  carbon,  and  heated  to  1000-1300°  C.  In  like 
manner,  Nauss  (B.P.  2298/10)  passes  coal  gas  over  nickel 
at  250-300°  C.,  whereby  the  carbon  monoxide  is  converted 
into  methane  which  is  subsequently  decomposed  by  treat- 
ment with  coke  at  1000-1200°  C.  According  to  Dieffen- 
bach  and  Moldenhauer  (D.R.P.  229406/09),  hydrocarbons 
mixed  with  steam  are  heated  and  passed  through  a  catalyst 
consisting  of  gauze  of  nickel,  platinum,  etc.,  disposed  at 


HYDROGEN  191 

right  angles  to  the  current ;  it  is  claimed  that  with  such  short 
exposure  to  the  catalyst  carbon  dioxide  is  formed  without 
the  production  of  carbon  monoxide.  Oxygen  may  be  added 
to  maintain  the  temperature. 

We  will  next  consider  a  series  of  patents  by  Pictet,  who 
in  B.P.  24256/10  prescribes  the  passage  of  acetylene,  alone 
or  mixed  with  other  hydrocarbons,  under  slight  positive 
pressure,  through  a  conduit  maintained  by  cooling  at  about 
500°  C.  If  liquid  hydrocarbons  are  added  to  the  acetylene, 
the  cooling  may  be  effected  by  their  evaporation.  The  heat 
evolved  by  the  decomposition  of  the  acetylene  serves  for  the 
decomposition  of  the  exothermic  hydrocarbons  added. 
According  to  B.P.  13397/11,  petroleum  is  distilled  into  a  long 
tube  maintained  at  1200-1350°  C.  by  the  supply  of  a  certain 
number  of  calories,  while  in  an  addition  to  this  patent,  namely 
B.P.  14703/11,  the  admixture  of  steam  with  the  petroleum 
is  prescribed,  so  that  the  carbon  is  wholly  or  partially  con- 
verted into  carbon  monoxide.  B.P.  16373/11  relates  to  the 
addition  of  oxygen  to  the  steam-petroleum  mixture.  The 
combination  of  the  carbon  and  oxygen  give  sufficient  heat 
to  enable  the  reaction,  represented  by  the  following  equation, 

C  +  H2O  =  CO  +  H2  —  29,100  calories, 

to  proceed.  The  products  in  the  two  last  patents  are  naturally 
mixtures  of  hydrogen  and  carbon  monoxide. 

Bosch,  in  D.R.P.  268291/11,  describes  the  continuous 
decomposition  of  acetylene  under  pressure.  B.P.  12978/13 
(Badische  Co.)  relates  to  the  passage  of  a  mixture  of  hydro- 
carbons and  steam  over  a  catalyst  consisting  of  a  medium 
such  as  magnesia  carrying  2-5  %  nickel  and  maintained  at  a 
temperature  of  800-1000°  C.  The  carbon  monoxide 
formed  is  subsequently  removed.  The  B.A.M.A.G.  (B.P. 
2054/14)  proposes  to  improve  upon  the  usual  practice, 
in  the  process  for  manufacturing  hydrogen  by  cracking 
oils  in  a  mass  of  heated  coke,  of  spraying  the  oil  on  the  coke, 
by  effecting  evaporation  of  the  oil  in  an  external  chamber 
heated  by  the  waste  gases  from  the  generator  during  the 
heating  phase.  Deposition  of  difficultly  combustible  carbon, 


192  INDUSTRIAL  GASES 

which  may  choke  up  the  generator,  is  thus  avoided.  Ellis 
(U.S. P.  1092903/14)  proposes  to  add  lime  to  the  fuel  in  order 
to  flux  the  ash  and  prevent  clinkering  difficulties,  while 
Brownlee  and  Uhlinger  (B.P.  5098/15)  describe  a  chamber 
which  contains  refractory  material  and  is  alternately  heated 
with  fuel  gases  and  used  to  decompose  hydrocarbons,  the 
carbon  formed  being  carried  along  with  the  hydrogen. 

The  principal  processes  which  are  known  to  be  in 
actual  operation  are  the  Carbonium  Gesellschaft,  Rincker 
and  Wolter,  Oechelhauser,  and  B.A.M.A.G.  (Bunte)  pro- 
cesses. 

Carbonium  Gesellschaft  Process. — In  this  process 
which  is  founded  on  the  patent  of  Machtolf  (see  p.  190) 
acetylene  is  compressed  to  about  2  atmospheres  and  ignited 
electrically.  Complete  decomposition  takes  place  with 
production  of  lampblack  which  is  separated  and  forms  a 
valuable  pigment,  about  60  Ibs.  per  1000  ft.3  of  hydrogen 
being  formed.  After  passing  through  large  scrubbers  the 
hydrogen  is  obtained  in  an  exceptionally  pure  state.  The 
commercial  success  of  the  process  depends  on  a  market  for 
the  lampblack.  A  Zeppelin  station  at  Friedrichshafen  was 
supplied  with  hydrogen  made  in  this  way. 

That  the  process  is  not  free  from  danger  is  evidenced  by 
the  fact  that  this  factory  was  largely  destroyed  by  an 
explosion  in  1910.  The  cost  (pre-war)  of  the  hydrogen  by 
this  process  is  stated  by  Sander  to  be  about  4/-  per  1000 
ft.3 

Rincker  and  Wolter  Process. — This  method  of  making 
hydrogen  is  due  to  two  Dutch  chemists,  Rincker  and  Wolter, 
and  has  been  developed  by  the  B.A.M.A.G.  and  the 
Hollandsche  Residugas-Maatschaapij.  Two  generators  of 
the  producer  type  are  filled  with  coke.  After  heating  the  fuel 
beds  to  a  high  temperature  by  an  air  blast,  the  air  producer 
gas  from  one  generator  being  burnt  by  secondary  air  in  the 
other,  tar,  oil,  or  other  cheap  hydrocarbon  is  sprayed  in  at 
the  top  of  each  generator  for  about  a  minute  ;  decomposition 
is  complete  in  about  20  minutes,  the  hydrogen  escaping  at 
the  bottom.  The  "  blow  "  is  then  repeated,  this  time  in 


HYDROGEN  193 

f 

the  reverse  direction.  The  carbon  formed  during  the  "make " 
is  deposited  on  the  coke  and  is  burnt  out  in  the  next  "  blow  " 
period.  After  traversing  a  system  of  scrubbers,  coolers  and 
driers,  hydrogen  of  the  following  percentage  composition  is 
.obtained  (Kills)  :— 

Hydrogen          . .          . .     96 
Nitrogen  . .         . .       1-3 

Carbon  monoxide        . .       27 

By  a  further  purification  with  heated  soda-lime  an 
analysis  as  below  is  obtained  : — 

% 
Hydrogen          . .          . .     98*4 

Nitrogen  . .          . .       i'2 

Carbon  monoxide        . .       0*4 

A  plant  producing  3500  ft.3/hr.  is  stated  to  cost  ^550 
exclusive  of  erecting  expenses  (Ellis),  while  the  hydrogen 
costs  2/6~4/-  per  1000  ft.3  (pre-war).  Plants  are  usually 
arranged  to  work  normally  for  the  production  of  illuminating 
gas,  and  for  hydrogen  manufacture  when  required.  Portable 
plants  on  the  Rincker  and  Wolter  system  have  been  used  by 
the  Russian  and  German  Air  Services.  Two  generators  lined 
with  firebrick  are  employed  and  are  mounted  on  two  railway 
trucks  together  with  a  turbo-blower  and  oil  pump  ;  the 
plants  have  a  capacity  of  about  3500  ft.3/hr.  Some  2-3 
hours  are  required  to  start  up  ;  only  coke  and  oil  are  used 
as  raw  materials,  while  two  men  are  sufficient  to  operate 
the  plant. 

Oechelhauser  Process. — This  process,  as  to  the  com- 
mercial operation  of  which  little  has  been  published,  depends 
on  passing  coal  gas  through  vertical  or  horizontal  retorts 
heated  to  1200°  C.  and  filled  with  coke.  The  lampblack 
formed  is  partly  deposited  on  the  coke  and  partly  carried 
along  with  the  hydrogen  wherefrom  it  is  filtered  by  wood  fibre. 
After  cooling  and  purification  the  gas  consists  of  80-84  % 
hydrogen.  The  following  analysis  indicates  the  nature  of 
the  changes  induced  (I/epsius,  Monit.  Sclent.,  (1912), 
493)  :— 

A.  I3 


INDUSTRIAL   GASES 


Coal  gas. 

Product  of  process. 

Heavy  hydrocarbons,  carbon  dioxide, 

% 

/o 

oxygen  and  nitrogen 

7-8 

— 

Carbon  monoxide 

5'  3 

7'  3 

Methane 

24-7 

6-9 

Hydrogen 

80-7 

The  cost  of  production  of  this  impure  hydrogen  is  stated 
by  L,epsius  to  be  about  the  same  as  that  of  the  original  coal 
gas  since  there  is  an  expansion,  or  about  2/9-3/6  per  1000 
ft.3  (pre-war). 

On  a  modification  of  this  method  of  making  hydrogen 
is  based  the 

B.A.M.A.G.  (Bunte)  Process. — This  process,  arising 
out  of  experiments  by  Bunte,  is  similar  to  the  Oechelhauser 
process.  Coal  gas  is  freed  from  carbon  dioxide  and  led 
over  white-hot  coke.  After  removing  carbon  monoxide 
by  soda-lime  the  product  is  stated  to  be  almost  pure 
hydrogen,  containing  only  a  little  nitrogen.  The  nitrogen 
content,  however,  will  be  not  less  than  that  originally  present 
in  the  coal  gas,  making  due  allowance  for  the  increase  in 
volume.  Crude  hydrogen  may  be  readily  manufactured  in 
this  way  in  ordinary  gas  works,  but  purification  by  soda-lime 
is  not  attractive  technically. 


MANUFACTURE  OF  HYDROGEN  BY  ELECTROLYSIS 

General. — Hydrogen  is  obtained  electrolytically  (i)  by 
the  electrolytic  decomposition  of  dilute  acids  or  alkalis 
as  a  special  operation,  or  (2)  as  a  by-product  in  certain 
electrochemical  operations,  e.g.  the  electrolysis  of  brine,  with 
the  production  of  caustic  soda,  the  electrolysis  of  fused  caustic 
soda  in  the  manufacture  of  sodium,  etc.  Since,  in  many 
cases  of  the  second  class,  the  plant  is  not  adapted  to  the 
collection  and  storage  of  all  the  gas  evolved,  the  hydrogen  is 
largely  wasted  ;  in  view  of  the  exceptional  purity  of  the  gas 
this  is  to  be  deplored. 

It  will  be  well  at  this  stage  to  give  some  of  the  constants 


HYDROGEN  195 

to  which  all  electronic  processes  for  decomposing  water 
may  be  referred. 

i  gram-ion 

96,470  coulombs  (ampere-seconds)  liberate  —  -2  -    -  —  grams  of  an  ion. 

valency  of  ion 


X  ionic  weight 
T  ampere-hour  liberates  -        alency  of  ion      -  grams  of  an  ion. 

418-6  c.c.  hydrogen  \  _f  N  T  p 
209-3  c.c.  oxygen   /  d 
441*6  c.c.  hydrogen)  at  15°  C.  and  760  mm. 
220-8  c.c.  oxygen    /      pressure. 
0-01560  ft.3  hydrogen^  at  15*  C.  and  760  mm. 
o  00780  ft.3  oxygen     /      pressure. 
,1000  ft.3  of  hydrogen  at  15°  C.  and  760  mm.  pressure  require  64,123 

ampere-hours. 
Decomposition  voltage  of  water  =  1*67  volts. 

1*67  is  the  lowest  voltage  at  which  a  permanent  current 
may  be  passed  through  water  and  consequently  determines 
the  minimum  possible  energy  expenditure,  namely  107*1 
K.W.H./iooo  ft.3  of  hydrogen  at  15°  C.  This  efficiency 
cannot  be  attained  in  practice,  however,  as  the  resistance  of 
the  electrolyte  necessitates  an  increase  in  the  voltage  to 
from  2  to  4  volts  according  to  the  electrolyte  and  the  con- 
struction of  the  cell,  thus  raising  the  energy  expenditure 
from  128  to  256  K.W.H./iooo  ft.3  of  hydrogen. 

It  may  be  stated  broadly  that  there  are  three  main 
aims  in  the  design  of  electrolytic  cells  :  (i)  to  obtain  the 
lowest  possible  resistance  ;  (2)  to  prevent  intermixing  of  the 
gases  ;  (3)  to  avoid  corrosion  of  the  component  parts  of  the 
cell.  These  problems  have  been  solved,  as  far  as  the  con- 
flicting nature  of  the  circumstances  allows,  as  follows  :  (i)  by 
using  short  columns  of  electrolytes  having  high  electrical 
conductivity,  the  heat  produced  by  the  resistance  of  the 
electrolyte  being  conserved  so  as  to  maintain  a  temperature 
of,  say,  70°  C.,  and  lower  the  resistance  ;  (2)  by  the  provision 
of  partitions  or  diaphragms,  porous  or  otherwise,  between  the 
electrodes,  or  by  the  provision  of  tortuous  paths  for  the 
current  in  the  electrolyte,  also  by  precautions  to  maintain 
equal  pressures  in  the  two  electrode  compartments  and 
(3)  by  suitable  selection  of  materials  and  electrolytes.  The 
conditions  for  (i)  and  (2)  are  somewhat  in  opposition  ;  thus, 
diaphragms,  etc.,  increase  the  resistance. 


196  INDUSTRIAL   GASES 

A  brief  survey  of  the  important  work  on  this  subject 
will  be  given  here  in  chronological  order  : — 

As  early  as  1881,  Barlow,  in  B.P.  1897/81,  proposed  the 
electrolysis  of  water,  while  d'Arsonval  (Elektrotech.  Zeits.,  12, 
(1891),    197)   produced   oxygen   for  physiological  purposes 
on  a  large  laboratory  scale  in  1885,  using  as  electrolyte  30  % 
caustic  potash  solution  with  a  linen  diaphragm.     Appar- 
ently the  first  large   scale   apparatus  was  constructed  by 
I,atchinoff  (B.P.  15935/88).     Either  an  acid  or  an  alkaline 
electrolyte  was  used,  with  asbestos  or  parchment  diaphragms. 
In  another  form  of  apparatus  lyatchmoff  introduced  the  use 
of  bipolar  electrodes  for  the  electrolysis  of  water.     He  also 
devised  an  apparatus  for  conducting  the  electrolysis  under 
a  pressure  of  120  atmospheres.     Renard  took  up  the  question 
from  a  military  standpoint  in  1888  (Soc.  de  Physique,  (1890), 
224  ;    D.R.P.  58282/90)  and  used  alkaline  electrolytes,  per- 
mitting the  use  of  iron  or  steel  electrodes.     A  further  advan- 
tage of  alkali  is  the  absence  of  ozone,  thus  permitting  the  use 
of  rubber   for   connections.     An   asbestos   diaphragm   was 
used,  an  B.M.F.  of  3  volts  being  required.     Inter-connected 
hydraulic  seals  were  employed  to  equalize  the  pressure  in 
the   anode   and   cathode   compartments.     In   1892   a   new 
principle  was  introduced  by  Garuti  (B.P.  16588/92)  in  the 
use  of  a  metal  partition  to  avoid  the  disadvantages  of  high 
resistance   and  frequent  renewals  associated  with  porous 
diaphragms.     The  metal  diaphragm  does  not  reach  to  the 
bottom  of  the  cell  and  the  E.M.F.  is  kept  below  that  at  which 
the  diaphragm  will  act  as  a  bipolar  electrode,  say  roughly 
about  3  volts.     The  apparatus  is  submerged  in  the  electro- 
lyte to  prevent  mixing  of  the  gases.     A  modification  of  this 
idea  is  embodied  in  the  patent  of  Siemens  and  Obach  (B.P. 
11973/93)  in  which  the  use  of  wire  gauze  diaphragms  is 
proposed.     Garuti  and  Pompili,  in  B.P.  23663/96,  also  try 
to  lower  the  resistance  by  the  use  of  diaphragms  perforated 
in  the  lower  parts.     In  1899  an  important  advance  was 
made  by  Schmidt  who,  in  D.R.P.  111131/99,  revived  the  idea 
of  bipolar  electrodes  in  combination  with  asbestos  diaphragms 
in  a  practical  way,  the  plant  taking  the  form  of  a  filter  press, 


HYDROGEN  197 

in  which  the  respective  gases  were  led  away  by  channels 
similar  to  those  in  filter-press  practice.  A  noteworthy 
economy  in  floor  space  is  thus  effected.  Schoop,  in  Austrian 
Patent  1285/1900,  describes  an  apparatus  which  dispenses 
with  a  continuous  diaphragm,  replacing  this  by  a  collecting 
bell  of  glass  or  clay  round  each  electrode.  We  find  another 
patent  by  Garuti  and^  Pompili,  B.P.  12950/1900,  where 
soldering  is  avoided  by  a  special  method  of  construction 
of  the  iron  cells.  The  cells  and  diaphragms  are  prolonged 
below  the  electrodes.  A  later  patent,  B.P.  2820/02,  relates 
to  covering  the  perforations  in  the  diaphragms  with  gauze, 
while  in  B.P.  27249/03,  the  same  inventors  describe  apparatus 
for  purification  of  the  gases  by  passing  them  over  heated 
platinum  wire.  In  B.P.  17981/06,  the  Elektrizitats  Aktien 
Gesellschaft,  vorm.  Schuckert  &  Co.  substitutes  for  the  usual 
diaphragm  an  insulated  bell  disposed  over  one  electrode, 
the  cell  forming  the  other  electrode  ;  in  later  patents,  B.P.s 
3000  and  3000A/07,  two  bells  are  used,  each  in  electrical 
connection  with  its  corresponding  electrode  and  separated 
from  the  other  by  a  screen  of  insulating  material  which 
projects  well  below  the  bells.  Cowper-Coles,  in  B.P.  14285/07, 
dispenses  with  diaphragms  and  uses  tongue-shaped  projections 
(pointing  downwards)  on  the  electrodes  as  guides  to  the 
gases,  while  B.P.  24716/09  by  Bycken,  I^eroy  and  Moritz 
deals  with  various  precautions  against  mixing,  especially 
when  the  gases  are  used  under  considerable  pressure,  in  an 
apparatus  of  the  filter-press  type,  the  outlets  being  con- 
trolled by  floats.  In  B.P.s  27264/10  and  21600/11, 
Knowles  describes  a  catalytic  purifier  with  heat  regenera- 
tion and  with  water  seals  supplied  by  the  water  produced 
in  the  purifier.  Electrolytic  plants  of  the  filter-press 
type  are  described  by  the  Soc.  Anon.  1'Oxhydrique  Fran- 
$aise  and  I^evin  in  B.P.s  18818/13  and  3654/14  respec- 
tively. The  recent  patents  on  this  subject  are  very 
numerous ;  it  will  perhaps  suffice  to  mention  the  following  : 
U.S.P.  1086804/14  by  Burdett,  D.R.P.  275515/14  by  Mas- 
chinenfabrik  Oerlikon,  B.P.  101598/16  by  Churchill  and 
Geeraerd,  and  U.S.P.s  1239530/17  and  1256067/18  by 


198  INDUSTRIAL   GASES 

Schriver,  as  examples  of  patents  which  have  been  developed 
commercially. 

Principal  Electrolytic  Processes  used  in  Practice 

The  best  known  processes  for  the  electrolytic  decompo- 
sition of  water  are  the  Schuckert,  Schmidt  (Oerlikon), 
Garuti,  Schoop,  Churchill,  International  Ox}-gen  Co.,  vSchriver 
and  Burdett  systems.  It  may  be  mentioned  that  electro- 
lysis, at  any  rate  in  the  past,  has  been  used  for  the  production 
of  oxygen  rather  than  hydrogen  except  as  regards  hydrogen 
for  military  purposes. 

Schuckert  Process. — In  the  Schuckert  apparatus  each 
cell  usually  takes  600  amperes.  The  electrodes  are  of  iron 
and  are  covered  with  iron  bells  insulated  from  the  electrodes 
and  separated  by  a  sheet  of  insulating  material.  As  electro- 
lyte a  20  %  caustic  soda  solution  is  used.  In  order  to 
minimize  the  resistance,  the  temperature  is  allowed  to  rise 
to  60-70°  C.  by  packing  round  with  sand,  when  2*8-3  volts 
are  required.  Some  corrosion  of  the  electrodes  takes  place 
necessitating  occasional  renewals.  For  a  plant  producing 
some  10,000  ft.3  of  hydrogen  per  day,  the  energy  expenditure, 
according  to  L,epsius  (Monti.  Sclent.,  (1912),  493),  costs  2/3  to 
1 1/3  per  1000  ft.3  hydrogen  plus  500  ft.3  oxygen,  while  the 
total  cost  (not  including  compression)  is  6/-  to  15/3  per 
1000  ft.3  hydrogen  plus  500  ft.3  oxygen,  when  electric  energy 
costs  0-1175^.  to  0*59^.  per  K.W.H.  By  calculation  from  the 
above  figures,  1000  ft.3  hydrogen  plus  500  ft.3  oxygen  require 
227  K.W.H.  According  to  Blum  (Metall.  and  Chem.  Eng., 
(1911),  157),  275  K.W.H.  are  required. 

This  process  is  stated  to  be  expensive  and  demands 
a  large  floor  space,  but  gives  very  pure  gases.  The  purity 
of  the  hydrogen  leaving  the  cells  is  about  99  %,  that  of  the 
oxygen  about  97  %.  The  gases  pass  through  scrubbers 
and  then  through  catalytic  purifiers. 

A  Schuckert  plant  was  installed  many  years  ago  by 
Herseus  of  Hanau  ;  there  are  plants  also  at  Kehl  am  Rhein, 
at  Metz,  at  the  Wolverhampton  works  of  the  British  Oxygen 
Co.  and  several  plants  in  the  United  States. 


HYDROGEN  199 

Schmidt  Process. — Schmidt's  multiple  cell'  takes  the 
form  of  a  filter-press  with,  for  example,  40  bipolar  electrodes 
in  series.  The  electrodes  are  separated  and  insulated  by 
asbestos  diaphragms,  reinforced  at  the  edges  with  rubber. 
By  means  of  passages  similar  to  those  in  a  filter-press,  the 
hydrogen  and  oxygen  respectively  are  led  to  the  two  sides 
and  pass  to  chambers  where  the  spray  is  separated  and  caused 
to  flow  back  to  the  bottom  of  the  cells.  The  gases  may  be 
taken  off  under  a  pressure  of  some  3  Ibs.  per  in.2,  or  even  up 
to  35  Ibs.  pressure,  this  being  advantageous  for  long  pipe 
lines.  This  plant  is  very  compact  and  free  from  complicated 
gas  and  current  connections.  The  electrolyte  is  a  10  % 
solution  of  potassium  carbonate  or  potassium  hydrate. 
An  B.M.F.  of  about  2*3  volts  per  cell  is  required  at  60°  C. 
According  to  L,orenz  the  current  efficiency  is  86  % .  Energy 
required  per  1000  ft.3  hydrogen  plus  500  ft.3  oxygen  is  about 
170  K.W.H.  according  to  Dammer  ;  at  0*25^.  per  K.W.H. 
the  cost  for  current  is  3/6.  Purification  is  effected  by  passing 
the  gases  over  platinized  asbestos  at  100°  C.  Traces  of  carbon 
monoxide,  derived  from  the  rubber  of  the  joints,  are  found  in 
the  oxygen.  The  purity  of  the  hydrogen  is  99  %,  that  of 
the  oxygen,  97  %.  A  Schmidt  plant  was  installed  by  the 
Swedish  Navy. 

The  manufacture  of  the  Schmidt  cell  was  taken  over 
by  the  Oerlikon  Co.,  who  installed  a  plant  at  the  Farnborough 
Air  Station,  cf.  p.  232.  Similar  apparatus  is  made  by  the 
International  Oxygen  Co.,  by  Schriver  and  Co.,  and  by 
other  firms  (see  below,  p.  200). 

Garuti  Process. — The  Garuti  cell  has  an  iron  diaphragm 
which  is  insulated  from  and  projects  below  the  electrodes, 
not  functioning  as  a  bipolar  electrode  so  long  as  the  voltage 
does  not  exceed  twice  the  decomposition  voltage  of  water 
or,  say  roughly,  3  volts.  The  absence  of  a  porous  diaphragm 
ensures  a  low  resistance,  while  to  decrease  this  still  further, 
the  diaphragms  are  perforated  opposite  to  the  centres  of  the 
electrodes,  the  holes  being  covered  with  gauze.  A  number 
of  narrow  cells  are  arranged  together  and  submerged  in  a 
tank  of  electrolyte,  a  hydraulic  seal  being  used  to  prevent 


200  INDUSTRIAL   GASES 

increase  of  pressure  and  mixing.  As  electrolyte,  26  % 
caustic  potash  solution  is  used.  The  gases  are  purified 
by  passing  over  heated  platinum  wire  ;  the  purity  attained 
is  98-99  %  for  the  hydrogen,  97  %  for  the  oxygen.  B.M.F. 
required  is  about  2*5  volts,  and  the  current  efficiency  about 
96  %  (Buff a).  Electrical  energy  per  1000  ft.3  hydrogen 
plus  500  ft.3  oxygen  is  therefore  167  K.W.H.,  and  cost  of 
this  at  0-25^.  is  3/6.  At  0-5^.  per  K.W.H.,  the  cost  per 
1000  ft.3  hydrogen  plus  500  ft.3  oxygen  is  stated  to  be  about 
9/-  uncompressed. 

Garuti  plants  have  been  installed  in  Rome,  Tivoli,  Terni, 
lyucerne,  Monthard,  and  by  the  American  Oxhydric  Co., 
Milwaukee,  Wis. 

Schoop  Process. — The  Schoop  process  employs  no 
diaphragm,  but  each  of  the  long  narrow  tubular  electrodes 
is  surrounded  by  a  collecting  tube  of  glass  or  clay.  Two 
anodes  and  two  cathodes  are  mounted  in  each  cylindrical 
cell.  Using  iron  and  an  alkaline  electrolyte,  the  voltage  is 
about  2 '25  volts,  or  if  lead  electrodes  and  dilute  sulphuric 
acid  are  used,  3*6  volts.  A  high  degree  of  purity  is  claimed 
for  the  gases,  namely,  hydrogen  97*5  %,  oxygen  99  %. 

With  an  acid  electrolyte,  which  is  apparently  most  com- 
monly used,  the  electrical  energy  per  1000  ft.3  hydrogen 
plus  500  ft.3  oxygen  for  a  voltage  of  3*6  and  a  current  effici- 
ency of  100  %,  would  be  230  K.W.H.,  costing  4/10  for  power 
at  o-25^./K.W.H. 

With  an  alkaline  electrolyte  and  a  voltage  of  2*25,  the 
power  would  be  144  K.W.H.,  the  cost  of  which  at  o'2$d./ 
K.W.H.  would  be  3/- ;  the  cost  of  the  plant  is  higher  in  this 
case. 

Plants  have  been  installed  at  Kalk  am  Rhein  and  else- 
where. 

International  Oxygen  Co.'s  Processes. — The  Inter- 
national Oxygen  Co.,  of  Newark,  N.J.,  has  two  well-tried 
systems  :— 

(i)  Bipolar  Filter-press  Type. — This  is  very  similar  to  that 
of  Schmidt ;  the  large  cells  use  a  current  of  400  amperes  at  a 
voltage  of  2,  a  set  of  60  electrodes  running  on  120  volts. 


HYDROGEN  201 

By  using  electrodes  of  commercially  pure  iron,  nickel-plated 
on  the  anode  side,  the  over-voltage  is  minimized.  The 
energy  is  guaranteed  not  to  exceed  127  K.W.H.  per  1000 
ft.3  hydrogen  plus  500  ft.3  oxygen  (measured  at  15°  C.  and 
760  mm.),  with  an  electrolyte  of  29  %  caustic  potash  solution. 
This  corresponds  to  a  cost  of  2/8  for  current  at  O'25^./K.W.H. 
As  electrolyte,  14*5  %  caustic  soda  solution  may  also  be  used. 
The  purity  of  the  hydrogen  is  stated  to  be  99*5  %  and  that 
of  the  oxygen  99  %  on  leaving  the  generators.  The  usual 
purifying  and  safety  devices  are  employed. 

(2)  Unit  Cell  Type. — Enclosed  oval  cells  are  used  with 
hydraulic  seals  for  the  cover  and  diaphragm,  the  latter 
being  of  asbestos.  The  tank  itself  forms  the  cathode,  and 
an  alkaline  electrolyte  is  used.  Energy  consumption  and 
purity  of  the  gases  are  very  similar  to  those  relating  to  (i). 

Other  Processes. — Apparatus  of  the  filter-press  type  is 
constructed  by  T.  Schriyer  and  Co.,  Harrison,  N.J.,  the 
performance  of  the  plant  is  very  similar  to  that  described 
above  for  the  International  Oxygen  Co.  type  (i). 

The  Churchill  apparatus  consists  of  narrow  cells,  the  walls 
of  which  form  the  electrodes.  No  diaphragm  is  employed 
and  intermixing  of  the  gases  is  prevented  by  the  provision 
of  a  series  of  glass  or  earthenware  vanes  arranged  close  to  the 
electrode  walls  at  an  angle  of  about  45°,  pointing  downwards. 
The  electrodes  may  be  provided  with  vertical  grooves  to 
allow  of  the  escape  of  the  gases  past  the  vanes.  Owing  to 
the  absence  of  a  diaphragm,  the  cell  has  a  low  resistance, 
and  works  at  2*3  volts.  The  energy  requirements  are  about 
155  K.W.H.  per  1000  ft.3  hydrogen  plus  500  ft.3  oxygen. 

The  Burdett  plant  has  a  number  of  electrodes  in  a  tank, 
and  the  gases  are  taken  off  by  means  of  bells  divided  into 
compartments  by  asbestos  diaphragms. 

In  the  above  processes  an  addition  of  distilled  water  is 
made  daily  to  compensate  for  that  decomposed  ;  about  4! 
gallons  are  required  per  1000  ft.3  of  hydrogen  neglecting 
evaporation.  With  alkaline  electrolytes,  absorption  of 
carbon  dioxide  is  largely  prevented  by  the  layer  of  water 
vapour  on  the  surface  when  warm,  or  a  layer  of  oil  may  be 


202  INDUSTRIAL   GASES 

used.  Those  systems  employing  light  gauge  electrodes, 
as  the  Garuti  and  Schuckert  types,  are  liable  to  corrosion 
of  the  anodes  at  high  current  densities  possibly  due  to  the 
presence  of  chlorides  or  sulphates  in  the  alkali.  Such  corrosion 
increases  the  resistance,  while  iron  may  be  deposited  on  the 
cathode  and  cause  short-circuiting. 

It  may  be  stated  in  general  that  the  production  of  hydro- 
gen by  the  electrolytic  decomposition  of  water  is  expensive 
compared  with  other  processes  unless  a  very  cheap  source 
of  energy  is  available  ;  further,  a  very  large  floor  space  is 
required.  The  purity  of  the  gases,  after  passing  over  a  heated 
catalyst,  is  very  high  (cf.  p.  213),  and  provided  that  due 
precautions  are  taken  against  intermixing,  the  process  is 
safe  and  requires  little  attention.  The  prevention  of  mixing 
is  very  important  when  the  gases  are  compressed,  and  several 
cylinder  explosions  have  been  traced  to  neglect  in  this 
particular  (cf.  also  p.  39  et  scq.).  Injury  to  the  diaphragm, 
blockage  in  the  system,  excess  voltage  on  cells  of  the 
Garuti  type,  or  too  great  current  density,  may  cause  such 
mixing. 

The  question  of  automatic  apparatus  for  the  detection 
and  estimation  of  oxygen  in  hydrogen  or  vice  versa  is  dis- 
cussed on  p.  33. 

Danger  Limits  as  regards  Intermixing  in  Electro- 
lytic Hydrogen  and  Oxygen. — The  inflammability  of 
mixtures  of  hydrogen  and  oxygen  depends  to  a  considerable 
extent  on  the  mode  of  ignition,  but  the  limits  may  be  taken 
as  5*3  %  oxygen  and  5 '5  %  hydrogen  in  hydrogen  and  oxygen 
respectively  (Fischer  and  Wolf,  Ber.,  44,  (1911),  2956). 
According  to  Burrell  and  Gauger  (loc.  cit.,  p.  40)  the  effect 
on  the  explosive  limits  of  increased  pressure  up  to  100 
atmospheres  is  very  small  (cf.  also  p.  40). 

Hydrogen  as  a  By-Product 

Hydrogen  is  produced  in  large  quantities  as  a  waste 
product  in  certain  electrochemical  industries,  e.g.  in  the 
Castner-Kellner  and  other  processes  for  the  manufacture  of 
caustic  soda  by  the  electrolysis  of  brine.  In  the  electrolysis, 


HYDROGEN  203 

a  volume  of  7230  ft.3  of  hydrogen  at  15°  C.  is  theoretically 
produced  per  ton  of  sodium  chloride  electrolysed.  The 
Griesheim-Elektron  works  at  Bitterfeld  and  Rheinfelden 
produced,  according  toL,epsius  (1911),  some  250,000,000  ft.3, 
i.e.  about  600  tons,  of  hydrogen  per  annum,  or  700,000  ft.3 
per  diem,  enough  to  inflate  a  dirigible  balloon  of  moderate 
size.  The  purity  of  the.  hydrogen  is  90-97  %.  If  ingress  of 
air  and  chlorine  be  prevented,  the  hydrogen  is,  of  course,  of 
a  high  degree  of  purity. 

On  the  advent  of  the  Zeppelin  in  1898  the  gas  was 
collected,  hydrogen  from  this  source  becoming  a  commercial 
article.  Hydrogen  in  a  compressed  state  may  now  be 
obtained  in  England  from  the  Castner-Kellner  Co.,  whose 
daily  production  is  some  500,000  ft.3,  but  before  the  war, 
at  any  rate,  the  bulk  of  the  gas  was  wasted.  .  Some  of  the 
hydrogen  has  been  used  by  this  firm  for  the  production  of 
pure  hydrochloric  acid  for  analytical  purposes,  etc.,  by  direct 
combustion  with  the  chlorine  simultaneously  liberated.  This 
may  be  effected  either  by  actual  combustion  or  by  combina- 
tion in  the  presence  of  a  catalyst,  e.g.  charcoal.  Special 
precautions  are  necessary  to  prevent  intermixing  of  the  gases 
outside  the  combustion  chamber. 

OTHER  PROCESSES  FOR  THE  MANUFACTURE  OF 
HYDROGEN 

Before  leaving  the  manufacture  of  hydrogen  by  methods 
suitable  for  use  in  stationary  plants,  it  will  be  well  to  consider 
briefly  a  few  patents,  etc.,  which  do  not  fall  under  the  preced- 
ing general  headings  and  which,  although  in  most  cases  of 
little  commercial  importance,  are  mentioned  for  the  sake  of 
completeness.  Some  of  the  methods  are  also  of  interest  in 
connection  with  field  operations  (vide  infra}. 

By  the  Action  of  Acids  or  Alkalis  on  Metals. — The 
use  of  the  action  of  acids  on  iron,  zinc,  etc.,  has  been 
proposed  from  time  to  time,  the  expense  of  the  processes 
being,  in  general,  only  tolerable  where  valuable  by-products 
are  secured. 


204  INDUSTRIAL  GASES 

In  B.P.s  16277/96  and  15509/07,  Pratis  and  Marengo 
describe  apparatus  for  the  generation  of  hydrogen  from 
sulphuric  acid  and  iron.  Carulla,  inB.P.  23702/08,  proposes 
to  absorb  the  hydrochloric  acid  from  salt  cake  manufacture, 
by  means  of  towers  packed  with  iron  scrap,  the  ferrous  chloride 
liquor  being  worked  up  for  iron  oxide.  In  like  manner  Barton 
(B.P.  28534/10)  suggests  the  interaction  of  zinc  and  sulphuric 
acid,  the  zinc  sulphate  solution  being  used  to  produce  zinc 
carbonate  for  use  as  a  pigment  and  filler,  while  Bastwick 
(B.P.  10228/11)  uses  the  acid-zinc  generator  as  a  battery. 
B.P.  107807/16,  by  Becquefort  and  Deguide,  relates  to  the 
utilization  of  sodium  bisulphate  by  treatment  with  iron 
scrap.  Another  patent,  B.P.  25891/11,  by  the  Chemische 
Fabrik  von  Hey  den,  A.G.,  deals  with  the  production  of 
hydrogen  by  the  action  of  ammonia  on  alloys  of  the  alkali 
metals  in  a  finely  divided  state.  Further  details  referring 
to  such  methods  will  be  found  under  Field  Processes  in  the 
following  section. 

Separation  of  Hydrogen  from  Water  Gas  and  the 
like  by  Physical  Methods. — The  only  process  of  technical 
importance  coming  under  this  category  is  the  I/inde-Frank- 
Caro  process,  which  has  been  already  described. 

Among  other  suggested  processes  may  be  mentioned  that 
proposed  by  d'Arsonval  (Ann.  Chim.  et  Phys.,  [7],  26,  (1902), 
446),  based  on  the  experiments  of  Dewar,  who  showed  that 
coal  gas  could  be  freed  from  hydrocarbons  by  cooling  to  a 
suitable  temperature  with  liquid  air.  Mazza,  in  B.P.  12194/02, 
and  Elworthy,  in  B.P.  10581/06,  propose  to  effect  a  preliminary 
separation  of  hydrogen  and  carbon  monoxide  (water  gas) 
by  centrifugal  action,  final  purification  of  the  two  fractions 
being  carried  out  according  to  Elworthy  by  chemical  means, 
e.g.  by  cuprous  chloride  and  caustic  soda  (cf.  also  B.P. 
17946/05  by  Clamond) . 

Several  other  patents  deal  with  diffusion  methods.  Thus, 
in  B.P.  22340/91,  Pullman  and  Elworthy  describe  the 
production  of  a  mixture  of  hydrogen  and  carbon  dioxide 
by  passing  excess  superheated  steam  over  red-hot  coke 
and  subsequent  separation  of  the  gases  by  diffusion  through 


HYDROGEN  205 

diaphragms  of  plaster  of  Paris  or  porous  earthenware. 
Jouve  and  Gautier,  in  F.P.  372045/06,  deal  with  a  similar 
separation  of  the  constituents  of  water  gas  by  means  of 
unglazed  earthenware  ;  it  is  stated  that  the  percentage  of 
carbon  monoxide  is  reduced  from  25  %  to  4-4  %  by  a  single 
passage.  Cf.  also  Nussow,  D.R.P.  295463/13,  where  liquid 
(e.g.  water)  or  solid  diaphragms  are  used.  Snelling,  in 
U.S. P.  1174631/16,  in  the  separation  of  carbon  monoxide 
from  hydrogen  uses  a  septum  of  porous  earthenware  or 
alundun,  with  a  thin  coating  of  platinum  or  palladium, 
heated  to  above  800°  C.  The  operation  is  preferably 
conducted  under  pressure. 

Through  the  Intermediary  of  Formates.— A  number 
of  patents  relate  to  the  production  of  hydrogen  by  the 
decomposition  of  formates,  prepared  from  producer  gas  and 
the  like.  Thus,  Feldkamp,  in  B.P.  22225/05,  prescribes 
the  production  of  formates  from  producer  gas  by  the  action 
of  alkali  solutions  (cf.  pp.  248,  316),  and  subsequent  heating 
of  such  formates  with  production  of  oxalates  and  hydrogen. 
Similarly  the  Badische  Co.,  in  B.P.  30073/13,  and  Weise  and 
Rieche,  in  U.S. P.  1098139/14,  deal  with  the  production  of 
formates,  using  e.g.  20  %  caustic  soda  liquor  heated  under 
pressure,  with  subsequent  decomposition  of  the  formate, 
either  in  the  presence  or  absence  of  the  residual  nitrogen  ; 
in  this  way  (i)  a  mixture  of  nitrogen  and  hydrogen  (see  p.  207) 
or  (2)  hydrogen  is  obtained. 

Miscellaneous  Methods.— In  B.P.  2080/81,  Helouis 
describes  a  process  whereby  carbon  monoxide  is  removed 
from  water  gas  by  passing  over  calcium  sulphate  heated  to 
redness  : — 

CaSO4  +  4CO  =  CaS  +  4  CO2 

the  carbon  dioxide   being   absorbed   by  sodium  carbonate 
solution. 

Hutin,  in  B.P.  23370/94,  covers  an  alloy  of  sodium  and  a 
heavy  metal  with  a  layer  of  concentrated  sodium  hydrate 
solution,  the  water  content  of  which  is  maintained  by  supply- 
ing with  steam  above .  A  too  violent  reaction  is  thus  avoided . 


206  INDUSTRIAL   GASES 

According  to  L,ahousse,  in  F.P.  361866/05,  steam  is 
decomposed  by  passage  over  red-hot  barium  sulphide,  which 
is  subsequently  regenerated  by  the  reduction  of  the  resulting 
barium  sulphate  with  producer  gas  or  coal. 

The  Nitrogen  Co.,  N.Y.,  in  B.P.  17666/11,  prescribes  the 
production  of  hydrogen  by  the  action  of  molten  zinc, 
antimony,  tin,  etc.,  at  a  red  heat  on  steam.  The  metal  is 
regenerated  by  passing  the  oxide  into  a  solvent  where  it 
comes  into  contact  with  carbon  or  other  reducing  agent. 
According  to  Kendall,  in  B.P.  26896/12,  a  mixture  of  sodium 
chloride  or  potassium  chloride  with  molybdenum  is  heated 
and  treated  with  steam.  Hydrogen,  hydrochloric  acid  and 
alkali  molybdate  are  produced.  The  molybdenum  is 
regenerated  by  reduction  of  the  molybdate  with  coke  when 
carbon  monoxide  and  sodium  or  potassium  vapour  are  formed 
leaving  metallic  molybdenum.  Tungsten  may  be  used  in 
like  manner. 

Teissier  and  Chaillaux,  in  F.P.  447688/12,  propose  to 
manufacture  hydrogen  and  oxygen  as  follows  :  Barium 
sulphate  is  first  heated  to  a  red  heat  with  manganous  oxide 
when  reaction  (i)  takes  place.  On  raising  the  temperature 
to  a  white  heat  reaction  (2)  occurs,  and  on  treating  with 
steam  under  pressure,  reaction  (3)  results,  giving  the  original 
mixture  again  :  — 


(1)  BaSO4  +  4MnO  =  BaS 

(2)  4MnO2  =  4MnO  -f  2O2 

(3)  BaS  -f4H2O  ==  BaSO4 


Hooton  (B.P.  18007/14)  proposes  the  treatment  of  iron 
pyrites  with  steam,  whereby  the  ore  is  left  almost  free  from 
sulphur  while  a  mixture  of  hydrogen,  sulphuretted  hydrogen 
and  sulphur  dioxide  is  produced.  By  interaction  of  the 
sulphuretted  hydrogen  and  sulphur  dioxide  in  the  presence 
of  bog  iron  ore,  sulphur  is  deposited,  any  excess  of  sulphur 
dioxide  being  removed  by  alkali. 

Siemens  and  Halske,  in  D.R.P.  220486/10,  describe  a 
process  of  treating  calcium  carbide  with  steam  at  a  high 


HYDROGEN  207 

temperature,  whereby  hydrogen  is  liberated  as  represented 
in  the  following  equation  :— 

CaC2  +  5H2O  =  CaO  +  2CO2  +  5H2 

The  carbon  dioxide  is  removed  by  the  lime  resulting  from  a 
previous  operation,  and  a  high  degree  of  purity  of  the 
hydrogen  is  claimed. 

Production  of  a  Mixture  of  Nitrogen  and  Hydrogen 
for  use  in  Synthetic  Ammonia  Manufacture 

Reference  has  just  been  made  (p.  205)  to  the  production 
from  producer  gas  of  a  mixture  of  nitrogen  and  hydrogen. 
There  are  a  number  of  industrial  applications,  e.g.  the 
synthesis  of  ammonia  and  the  filling  of  electric  lamps,  in 
which  a  mixture  of  nitrogen  and  hydrogen  is  required,  and 
occasionally  it  may  be  convenient  to  produce  the  mixture  in 
a  single  operation.  Since  in  the  B.A.M.A.G.  continuous 
catalytic  hydrogen  process,  any  nitrogen  present  in  the 
water  gas  persists  in  the  hydrogen  produced,  it  is  obviously 
a  simple  matter  by  using  a  controlled  semi-water  gas  instead 
of  water  gas  to  produce  a  nitrogen-hydrogen  mixture  of 
any  desired  composition.  Similarly  in  the  L,ane  or  Messer- 
schmitt  process,  instead  of  steam,  as  in  the  usual  method  of 
operation,  a  suitable  mixture  of  air  and  steam  may  be 
passed  over  the  reduced  iron  (cf.  Dieffenbach  and  Molden- 
hauer,  B.P.  12051/12,  p.  177).  According  to  Messer- 
schmitt,  D.R.P.  291603/13,  if  steam  is  passed  first  and  air 
is  substituted  when  oxidation  is  partly  effected,  a  more 
complete  oxidation  of  the  iron  results.  As  described  in 
U.S. P.  1123394/15,  Scholl  obtains  a  mixture  of  nitrogen  and 
hydrogen  suitable  for  lamp  filling  by  passing  a  correctly 
proportioned  mixture  of  gaseous  ammonia  and  air  over  heated 
catalytic  material  (cf.  p.  113). 

METHODS  OF  FINAI,  PURIFICATION  OF  HYDROGEN 

Certain  methods  of  removal  of  foreign  constituents 
generally  present  only  in  small  quantities,  not  having  been 


208  INDUSTRIAL   GASES 

described  previously  under  the  various  methods  of   manu- 
facture, will  be  given  under  this  heading. 

Purification  from  Carbon  Monoxide 

The  elimination  of  carbon  monoxide  from  admixtures 
with  hydrogen  demands  special  treatment  as  the  ready 
oxidation  of  the  hydrogen  itself  precludes  the  application 
of  such  methods  as  the  simple  treatment  with  red-hot  copper 
oxide  used  for  nitrogen.  Generally  speaking,  the  high 
pressure  methods  described  are  only  economical  in  connection 
with  the  production  of  synthetic  ammonia. 

(10)  By  Soda-Lime. — In  B.P.  10164/89  Crookes  and 
Ricarde-Seaver  deal  with  the  removal  of  carbon  monoxide 
from  water  gas  by  soda-lime  at  a  red  heat.  At  this  tem- 
perature carbonate  is  formed  but  the  reaction  may  be  carried 
out  more  advantageously  at  a  lower  temperature,  e.g.  180°  C., 
with  the  production  of  formate,  the  absorption  of  carbon 
monoxide  being  facilitated  by  the  use  of  pressure. 

(ib)  By  Caustic  Soda  Solution. — B.P.  1759/12,  by  the 
Badische  Co.,  relates  to  the  removal  of  the  last  traces  of 
carbon  monoxide  from  hydrogen,  containing,  say  i  %,  by 
passing  through  a  solution  of  caustic  soda  at  a  temperature 
of  240-260°  C.  under  a  pressure  of  from  50  to  200  atmo- 
spheres. The  reaction  is,  of  course,  the  same  as  that 
occurring  with  soda-lime.  The  resulting  sodium  formate 
is  a  valuable  by-product,  cf.  applications  of  carbon 
monoxide,  p.  248. 

(2)  By  Cuprous  Chloride  Solution. — Huntingdon,  in  B.P. 
15310/84,  deals  with  the  removal  of  carbon  monoxide  from 
producer  gas  by  the  action  of  ammoniacal  cuprous  chloride 
solution  under  pressure,  the  copper  solution  being  freed  from 
gas  by  subjecting  to  a  vacuum.  Cf.  also  Williams,  B.P. 
19096/89.  The  use  of  alternate  application  of  pressure  and 
the  release  of  the  same  is  also  claimed  by  lyinde  in  D.R.P. 
289106/14.  A  series  of  patents  by  the  Badische  Co.  follows. 
In  B.P.  8030/14  are  described  special  solutions  of  cuprous 
chloride  which  do  not  attack  iron,  containing  at  least  6  % 
of  ammonia,  either  free  or  as  carbonate,  for  use  in  steel 


HYDROGEN  209 

vessels  under  high  pressure.  B.P.  9271/14  deals  with 
the  employment  for  a  similar  purpose  of  ammoniacal  cuprous 
solutions  containing  little  or  no  halogen.  Weak  acids,  such 
as  acetic,  may  be  present.  According  to  a  further  patent, 
B.P.  20616/14,  the  addition  of  oxygen  is  prescribed  in  the 
use  of  ammoniacal  cuprous  solutions  to  prevent  the  separa- 
tion of  copper  and  also  .to  effect  oxidation  of  part  of  the 
carbon  monoxide  to  carbon  dioxide. 

(3)  By  Conversion  into  Methane. — It  is  a  simple  matter 
to  remove  small  quantities  of  carbon  monoxide  by  conversion 
into  methane  ;  this  is  only  useful  in  cases  where  the  presence 
of  a  little   methane   is  not  detrimental.     The   conversion 
is  effected  by  means  of  a  nickel  catalyst  at  a  temperature 
of  250-300°  C.  (cf.  p.  240). 

(4)  By  Calcium  Carbide. — Claim  is  made  by  Frank,  in  B.P. 
26808/06,  for   the   purification   of   hydrogen    from   carbon 
monoxide,  carbon  dioxide,  nitrogen  and  hydrocarbons  by 
passage  over  calcium  carbide  at  a  temperature  over  300°  C. 
(Actually  a  much  higher  temperature  than  300°  C.  is  required.) 
The  carbide  may  be  mixed  with  other  substances  to  promote 
the  action.     A  later  patent,  B.P.  26928/06,  prescribes  a  pre- 
liminary  purification    from   oxides  of    carbon    and    other 
impurities  before  this  treatment. 

Purification  from  Carbon  Dioxide 

Carbon  dioxide  is  an  impurity  the  removal  of  which  from 
hydrogen  is  often  necessary,  and  a  brief  summary  of  the 
different  methods  proposed  will  be  useful. 

Small  quantities  of  carbon  dioxide  may  be  removed  by 
ordinary  lime  purifiers,  i.e.  boxes  containing  trays  of  slaked 
lime  ;  if  larger  amounts  are  present,  other  methods  are 
preferable,  the  most  important  being  dependent  on  the 
action  of  water  under  pressure. 

In  B.P.  1471/73  Baggs  claims  the  removal  of  carbon 
dioxide  by  washing  with  water  or  sodium  carbonate  solution 
underpressure,  and  L,ane,  in  B.P.  11878/10,  abstracts  carbon 
dioxide,  sulphuretted  hydrogen  and  sulphur  dioxide  from 
hydrogen  by  water  under  a  pressure  of  several  atmospheres, 
A.  14 


210  INDUSTRIAL   GASES 

the  energy  of  the  released  water  being  utilized.  A  process 
described  by  Claude,  in  B.P.  15053/14,  depends  on  the  use 
of  lime-water  instead  of  water  in  the  pressure  absorption. 
By  adopting  a  counter-current  system  the  final  purification 
is  effected  by  alkali  and  the  initial  treatment  by  water. 

In  the  use  of  water  under  pressure,  it  is  usually  necessary 
to  complete  the  action  with  caustic  solution,  preferably  also 
under  pressure.  Reference  has  already  been  made  to 
the  removal  of  carbon  dioxide  by  the  Bedford  process  of 
scrubbing  with  water  under  pressure  in  connection  with  the 
B.A.M.A.G.  continuous  catalytic  process  and  the  lyinde- 
Frank-Caro  process  for  the  manufacture  of  hydrogen. 

Solution  may  also  be  effected  by  ammonia  liquor  (Claus, 
B.P.s  15173/88  and  50/89),  or  by  alkali  carbonate  or  alkaline 
earth  carbonate  solutions  (Reissig  and  L,andin,  B.P.  2021/91), 
the  carbon  dioxide  being  subsequently  expelled  by  heating, 
reduced  pressure  being  also  employed  in  the  case  of  carbon- 
ate solutions,  cf.  pp.  264-8. 

Purification  from  Sulphur  Compounds 

Sulphuretted  hydrogen  may  be  removed  to  a  considerable 
degree  of  completeness  by  treatment  with  bog  iron  ore  in 
purifiers  such  as  are  used  in  ordinary  gas  works  practice. 
Several  patents  have  been  brought  forward  with  the  object 
of  effecting  a  more  rigorous  purification,  e.g.  in  U.S. P. 
1034646/12,  Rabenalt  proposes  to  remove  sulphuretted 
hydrogen  by  passing  through  a  solution  of  iodine  which  is 
continuously  regenerated  by  means  of  an  electric  current. 
According  to  Pintsch,Strache  and  Killer, in  D.R.P.  286374/14, 
sulphuretted  hydrogen  is  removed  by  passing  rapidly  through 
an  ordinary  oxide  purifier  first  and  then  through  copper 
sulphate  solution.  The  residual  copper  sulphide  is  reoxidized 
to  sulphate  by  heating  in  air  of  oxygen  at  a  temperature 
sufficiently  high  to  prevent  separation  of  sulphur. 

The  removal  of  carbon  disulphide  and  organic  sulphur 
compounds  is  much  more  difficult  than  that  of  sulphuretted 
hydrogen.  Carbon  disulphide  can  be  partially  removed  by 
passage  through  foul  lime  (i.e.  Ca(SH)2)  as  in  ordinary  gas 


HYDROGEN  211 

works  practice,  but  the  process  is  very  unsatisfactory.  In 
B.P.  14509/13,  the  Badische  Co.  prescribes  the  action  of 
heated  caustic  soda  solution  under  a  pressure  exceeding 
5  atmospheres  for  the  removal  of  sulphur  compounds,  includ- 
ing organic  sulphur  compounds.  Thus,  a  temperature  of 
150-225°  C.  may  be  used  for  a  10-25  %  caustic  soda  solution 
at  50  atmospheres  (cf.  also  pp.  208,  250). 

A  very  interesting  process  has  been  evolved  by  Carpenter 
and  Evans  (B.P.  29673/10  ;  Trans.  Inst.  Gas  Eng.,  (1914),  183) 
in  connection  with  coal  gas  and  is  in  use  on  a  very  large 
scale  by  the  South  Metropolitan  Gas  Co.,  one  installation 
treating  15,000,000  ft.3/diem.  The  carbon  disulphide  is 
converted  into  sulphuretted  hydrogen  by  passing  the  gas 
over  reduced  nickel  at  a  temperature  of  about  430°  C.,  the 
sulphuretted  hydrogen  being  subsequently  absorbed  in  the 
usual  way.  The  carbon  disulphide  content  is  reduced  from, 
say  40  grains/ioo  ft.3,  or  0*029  %  by  volume,  to  about  1/5 
of  this  value.  Carbon  is  deposited  on  the  catalyst  and  is 
removed  by  the  periodic  passage  of  air  about  every  month. 

According  to  Guillet,  in  B.P.  18597/12  and  "  Soc.  Tech.  de 
1' Industrie  du  Gaz  de  France,"  (1912),  245,  carbon  disulphide 
may  be  removed  catalytically  by  passing  the  gas,  freed  from 
sulphuretted  hydrogen,  at  a  temperature  of  80-200°  C. 
in  the  presence  of  water  vapour  over  iron  oxide  which 
absorbs  the  sulphuretted  hydrogen  formed.  If  air  also  be 
added,  the  sulphuretted  hydrogen  and  the  carbon  disulphide 
may  be  removed  in  a  single  operation  ;  in  this  case  the  exit 
gases  are  preferably  washed  with  alkali.  In  B.P.  3752/10, 
Bedford  and  Williams  deal  with  the  removal  of  sulphur 
compounds,  etc.,  by  cooling  the  gas  to  — 190°  C.  The  removal 
of  sulphur  dioxide  is  effected  by  the  methods  given  above 
for  carbon  dioxide  and  will  take  place  at  the  same  time  if 
both  impurities  are  present. 

Purification  from  Other  Impurities 

The  removal  of  arseniuretted  hydrogen  has  been  proposed 
by  bubbling  through  petroleum  cooled  to  — 110°  C.  by  Renard 
(Comptes  Rend.,  136,  (1903),  1317),  and  according  to  Wentzki 


212  INDUSTRIAL   GASES 

(Chemisette  Industrie,  29,  (1906),  405)  the  same  object  may 
also  be  achieved  by  the  use  of  bleaching  powder  or  by  passing 
through  a  red-hot  tube  containing  copper  turnings. 

Reference  has  been  made  already  to  the  removal  of  small 
quantities  of  oxygen  in  connection  with  the  manufacture  of 
electrolytic  hydrogen  ;  when  the  absence  of  this  impurity 
is  desired,  it  is  very  readily  secured  by  passage  over  heated 
platinized  pumice  or  other  catalyst. 

Comparison  of  Costs  of  Production  and  Purity 
Attainable  by  the  Different  Methods 

The  following  table  will  serve  to  give  some  idea  of  the 
relative  merits  of  the  different  processes  from  an  economic 
standpoint.  The  costs,  which  are  on  a  pre-war  basis,  are  to 
be  regarded  as  rough  approximations  only.  Overhead 
charges  are  not  included.  The  low  prices  claimed  for  some 
of  the  processes  are  to  be  taken  with  reserve,  especially  for 
those  which  have  not  been  developed,  e.g.  the  Bergius 
process.  The  cost  of  electrolytic  hydrogen  is  conditioned  by 
the  very  variable  price  of  electric  energy  and  also  by  the 
credit  for  the  oxygen.  Reference  may  be  made  to  Table  25, 
giving  the  cost  of  production  by  various  "  Field  Processes." 

As  regards  purity,  values  have  also  been  inserted  in  the 
table.  Generally  speaking,  it  may  be  stated  that  the  electro- 
lytic process,  the  Carbonium  process  and  the  Bergius  process 
are  those  which  alone  give  hydrogen  of  a  high  degree  of  purity. 
Hydrogen  from  the  lyinde-Frank-Caro  process  is  quite  free 
from  sulphur  compounds,  while  that  made  in  the  B.A.M.A.G. 
continuous  catalytic  process  is  practically  equally  good  in 
this  respect.  In  both  processes,  however,  an  appreciable 
amount  of  carbon  monoxide  is  present,  as  is  also  the  case  in 
a  greater  or  less  degree  in  all  the  remaining  processes.  The 
nitrogen  content  is  of  special  importance  only  in  connection 
with  aeronautics,  in  diminishing  the  lifting  power  of  the  hydro- 
gen. All  the  usual  impurities  found  in  technical  hydrogen  have 
roughly  the  same  density  and,  consequently,  the  same  effect 
on  the  lifting  power.  The  impurity  of  most  importance  is 
carbon  monoxide,  especially  when  the  hydrogen  is  to  be  used 


HYDROGEN 


213 


for  the  manufacture  of  ammonia  by  the  Haber  process  and  in 
a  lesser  degree  when  used  for  the  hydrogenation  of  oils  (cf. 
"Applications  of  Hydrogen,"  p.  214). 

Taking  everything  into  consideration,  there  can  be  little 
doubt  that  the  B.A.M.A.G.  continuous  catalytic  process  is 
the  most  suitable  for  use  in  this  country  for  such  purposes  as 
the  production  of  synthetic  ammonia,  when  the  cost  of  the 
hydrogen  is  of  paramount  importance.  On  the  other  hand, 
the  purity  is  not  very  high  and  especially  for  ammonia 
synthesis,  further  purification  from  carbon  monoxide  is 
necessary.  Electrolytic  hydrogen  is  only  likely  to  be  a 
serious  competitor  in  places  where  cheap  water  power  is 
available.  For  aeronautical  purposes  the  L/ane  and  allied 
processes  are  probably  the  most  satisfactory,  as  giving  a  high 
percentage  of  hydrogen  at  a  moderate  cost ;  the  elimination 
of  nitrogen  from  the  gas  obtained  from  the  B.A.M.A.G. 
process  is  not  practicable. 

TABLE   23. 

COST  OF  PRODUCTION  AND  PURITY  OF  HYDROGEN  BY  DIFFERENT 
PROCESSES  (STATIONARY  PLANTS). 


Process. 

Cost  per 

IOOO  ft.3 

Shillings. 

Purity 
(%  hydrogen). 

Percentage  ot 
carbon 
monoxide. 

B.A.M.A.G.  continuous  catalytic 

process 

I'75 

ca.  92  % 

i'5-3-0 

Griesheim-Elektron  process 

2-3 

97'5  % 

0'2 

Linde-Frank-Caro  process 

3-4 

97% 

2 

Lane  process 

3-4 

98-5-99-5  % 

0-25-r5 

Messerschmitt  process    .  . 

2 

ca.  99  % 

0-25-r5 

Bergius  process 

lJ-2 

99-95  % 

O'OO  I 

Carbonium  process 

4 

very  pure 

— 

Rincker  and  Wolter  process 

2*-4 

96  % 

3 

Oechelhauser  process 

ca.  3 

80% 

7 

Electrolytic  processes,  with  cur 

rent  at  o-25^./K.W.H.,  assum 

ing  no  credit  for  oxygen 

3-4 

very  pure 

nil 

Applications  of  Hydrogen 

Apart  from  aeronautical  requirements,  the  chief  con- 
sumption of  hydrogen  in  this  country  is  in  connection  with 
the  hydrogenation  of  oils  and  fats  ;  the  synthetic  ammonia, 


214  INDUSTRIAL   GASES 

industry  also  has  assumed  importance  in  Germany  and  is 
being  developed  in  the  United  States. 

The  Hydrogenation  of  Oils  and  Fats. — In  1897,  a 
description  was  given  by  Sabatier  and  Senderens  of  a  general 
method  for  the  hydrogenation  of  organic  unsaturated  sub- 
stances (cf.  resume  by  Sabatier  and  Senderens,  Ann.  de 
Chim.  et  de  Phys.,  [8],  4,  (1905),  3*9  ;  *&<*•,  PL  16,  (1909), 
70  ;  also  Sabatier,  Ber.t  44,  (1911),  1984  ;  "  La  Catalyse  en 
Chimie  Organique,"  1913). 

Speaking  generally,  the  method  consists  in  passing  the 
organic  substance  in  the  state  of  vapour  accompanied  by 
hydrogen  over  gently  heated,  finely  divided  metals — nickel, 
cobalt,  iron,  platinum,  palladium  and  copper  being  the  most 
useful  and  their  respective  activities  somewhat  as  in  the 
order  given.  The  activity  of  the  catalyst  depends  on  its 
temperature  of  reduction,  e.g.  nickel  reduced  at  a  bright-red 
heat  is  practically  inactive,  whereas  when  reduced  at  250°  C. 
it  is  excessively  active  but  rather  sensitive  and  variable. 
300°  C.  is  a  generally  useful  reduction  temperature.  The 
catalysts  are  very  sensitive  to  traces  of  "  poisons,"  of  which 
the  most  important  are  sulphur,  chlorine,  arsenic,  antimony, 
and,  in  a  lesser  degree,  carbon  monoxide.  For  a  discussion 
of  the  inhibitive  action  of  carbon  monoxide,  see  pp.  19,  241. 
Sabatier's  work  was  carried  out  in  the  gaseous  phase,  and  the 
avoidance  of  any  liquid  in  contact  with  the  catalyst  is 
prescribed.  As  examples  may  be  cited  the  reactions  : 
CO  +  3H2  =  CH4  +  H20  and  C6H6  -f  3H2  =  C6H12 

The  application  of  the  method  to  liquids  is  due  to  the 
work  of  Paal,  Willstatter,  Ipatiew,  and  Skita  in  the  first 
instance,  while  the  technical  application  is  largely  due  to 
Norman  (1903).  The  hardening  of  oils  and  fats  consists 
in  the  conversion  of  the  glycerides  of  the  unsaturated  acids 
into  the  glycerides  of  the  corresponding  saturated  acids. 
The  effect  is  to  raise  the  melting  point  and  in  most  cases 
to  free  from  objectionable  odour,  taste  and  colour,  the 
market  value  being  considerably  enhanced.  According  to 
Schuck  (Chem.  Trade  J.,  63,  (1918),  139)  deodorization 
without  hardening  may  be  effected  by  the  use  of  hydrogen 


HYDROGEN  215 

without  a  catalyst.  Whale  oil  is  one  of  the  principal  oils 
hardened  ;  a  certain  factory  in  Norway  is  capable  of  hardening 
some  55,000  tons  of  whale  oil  per  annum,  using  electrolytic 
hydrogen.  Some  35,000  ft.3/hr.  of  hydrogen  from  the  lyinde- 
Frank-Caro  process  alone,  are  used  for  fat  hardening,  equiva- 
lent to  about  100,000  tons  of  fat  per  annum,  one  ton  of 
triolein,  for  example,  requiring  about  2700  ft.3  of  hydrogen. 
The  hardened  fats  are  extensively  used  as  edible  fats  and  in 
the  manufacture  of  soap,  candles,  etc. 

The  catalyst  usually  employed  is  nickel,  although  palla- 
dium is  sometimes  used.  According  to  some  systems  nickel 
from  the  sulphate  is  precipitated  as  carbonate  in  the  presence 
of  kieselguhr,  the  mixture  filtered,  the  cake  dried,  finely 
powdered,  calcined  to  convert  the  nickel  carbonate  into 
oxide,  then  reduced  in  hydrogen  and  allowed  to  fall 
without  contact  with  air  into  oil  with  which  it  is  intimately 
mixed.  This  mixture  is  added  in  the  desired  proportions  to 
the  oil  to  be  hardened  ensuring,  e.g.  0*5-1  part  of  nickel 
to  100  parts  of  the  oil,  which  is  carefully  dried  before  using. 
Temperatures  in  the  neighbourhood  of  150-250°  C.,  with 
pressures  of  5-15  atmospheres,  are  employed.  Instead  of 
metallic  nickel  the  suboxide  may  be  used.  For  a  discussion 
of  the  constitution  of  nickel  catalysts,  see  Erdmann,  /.  Prakt. 
Chem.,  91,  (1915),  469.  After  the  hydrogenation  the  catalyst 
is  removed  by  filtration  and  used  again.  The  products  always 
contain  minute  traces  of  nickel.  The  above  remarks  relating 
to  catalyst  poisons  apply  equally  to  treatment  of  liquids. 
According  to  Ellis  (U.S.P.  1247516)  the  poisons  present  in 
the  oil  may  be  removed  by  preliminary  treatment  with 
copper  hydroxide.  For  an  account  of  modern  developments 
in  the  manufacture  of  edible  fats,  cf.  Clayton,  /.  Soc.  Chem. 
Ind.,  (1917),  1205. 

The  Manufacture  of  Synthetic  Ammonia.— The 
synthetic  ammonia  industry  in  Germany  has  been  developed 
from  the  work  of  Haber  and  collaborators  and  ranks  as  one 
of  the  finest  achievements  arising  out  of  the  application  of 
physico-chemical  methods  to  industry  : 

N2  -f  3H2  =  2NH3  -f- 11,000  calories. 


2l6 


INDUSTRIAL   GASES 


Many  experimenters  had  previously  attempted  to  effect 
the  synthesis  of  ammonia,  but  without  much  success  ;  an 
approximate  calculation  of  the  equilibrium  constant 


3H2  X  P*2 

by  the  Nernst  Heat  Theorem  is  sufficient  to  show  that  only 
a  very  small  percentage  of  ammonia  can  exist  at  temperatures 
for  which  suitable  catalysts  were  at  that  time  known,  e.g. 
800°  C. 


Since 


where  P  is  the  total  pressure,  it  is  evident  that  the  concen- 
tration of  the  ammonia  is  almost  directly  proportional 
to  the  pressure.  Such  considerations  led  Jost  and,  at 
about  the  same  time,  Haber  and  I^e  Rossignol  to  study 
the  effect  of  high  pressures,  and  the  latter  investigators 
worked  out  a  series  of  catalysts  which  enabled  equilibrium 
to  be  attained  fairly  rapidly  at  temperatures  as  low  as 
300°  C. 

The  following  table  shows  the  influence  of  temperature 
on  the  equilibrium  values  :— 

TABLE   24. 
EQUILIBRIA  IN  THE  SYNTHESIS  OF  AMMONIA. 


Percentage  of  ammonia  at  absolute  pressures  of — 


lemperaiure    v^. 

i  atm. 

100  alms. 

200  atms. 

200 

I5'3 

80-6 

85-8 

300 

2-18 

52'  i 

62-8 

400 

0-44 

25-1 

36-3 

500 

O-I29 

10-4 

17-6 

600 

0-049 

4-47 

8-25 

700 

O-O223 

2-14 

4-11 

800 

O'OIiy 

i'i5 

2-24 

QOO 

0-0069 

0-68 

i'34 

IOOO 

0-0044 

o-44 

0-87 

HYDROGEN 


217 


The  advantage  of  the  higher  equilibrium  values  can  be 
only  partly  turned  to  account  by  reason  of  the  accompanying 
decrease  of  the  reaction  velocity.  At  very  high  temperatures, 
a  reversal  of  the  equilibrium  sets  in  (cf.  Maxted,  Chem. 
Soc.  Trans.,  (1918),  168,  386;  ibid.,  (1919),  113),  thus  by 
passing  a  mixture  of  nitrogen  and  hydrogen  through  a  capil- 
lary tube  in  which  a  high  tension  arc  was  burning  under  a 
pressure  of  i  atmosphere,  an  ammonia  content  in  the  exit 
gases  as  high  as  2*0  %  was  observed. 

As  in  other  heterogeneous  gas  reactions,  a  rise  in  the  velocity 
of  passage  of  the  gases  over  the  catalyst  has  the  effect  of 
lowering  the  percentage  of  ammonia,  but  of  increasing  the 
production  ;  this  is  a  matter  of  considerable  importance 
as  when  using  high  pressures  the  available  space  for  the 
catalyst  is  necessarily  limited. 

As  an  example  of  this  behaviour  may  be  cited  the 
following  results  obtained  at  a  working  pressure  of  114 
atmospheres  and  with  a  catalyst  temperature  of  515°  C.,  the 
catalyst  employed  being  uranium  carbide  (Haber  and  Green- 
wood, Z.  Elektrochem.,  21,  (1915),  241)  : — 


Space  velocity  (litres  of  free 

gas  /  litre    catalyst    space  / 

hour) 

5800 

31,650 

82,600 

194,000 

Percentage    of   ammonia   by 

volume 

7  63 

6'42 

4-78 

4-18 

Space-time-yield    (kilos,    am- 

monia/litre catalyst  space/ 

hour)           .  .          .  . 

0-318 

1*46 

2-84 

5-83 

It  should  be  pointed  out,  however,  that  the  above  con- 
siderations are  not  the  only  deciding  factors,  as  the  space- 
velocity  is  limited  by  such  considerations  as  regeneration 
of  heat,  ammonia  absorption,  etc. 

Amongst  the  most  efficient  catalysts  may  be  mentioned 
metallic  osmium  and  uranium  carbide,  the  range  of  useful 
working  temperature  being  500-700°  C.  The  process  was 
subsequently  taken  over  and  developed  by  the  Badische 
Anilin  und  Soda  Fabrik. 

Since  the  percentage  of  the  gases  undergoing  conversion 


2i8  INDUSTRIAL   GASES 

is  only  relatively  small  even  at  the  pressures  employed,  f.g. 
100  to  200  atmospheres,  it  is  necessary  to  circulate  the 
gases  through  the  catalyst  removing  the  ammonia  without 
releasing  the  pressure,  and  passing  again  over  the  catalyst 
reinforced  with  a  fresh  supply  of  nitrogen-hydrogen  mixture 
to  replace  the  portion  converted.  The  ammonia  formed  is 
removed  from  the  system  either  by  cooling  or  by  absorption 
with  water. 

As  regards  catalysts,  osmium  is  too  expensive  and  too 
limited  in  amount  for  use  on  the  large  scale,  while  uranium 
is  very  sensitive  to  traces  of  oxygen  or  moisture  (cf.  Haber 
and  Greenwood,  loc.  cit.).  So  far  as  can  be  gathered  from 
the  patent  literature,  the  catalysts  used  in  practice  have  a 
basis  of  pure  iron  with  the  addition  of  a  promoter.  Among 
such  promoters  may  be  mentioned  potassium  oxide,  lime, 
magnesia,  alumina,  zirconia,  molybdenum,  vanadium  and 
cobalt  as  patented  by  the  Badische  Co.  Other  patented 
catalyst  groups  are  various  alkali  and  alkaline  earth  ferro- 
cyanides  (F.  Bayer  &  Co.) ;  ruthenium  and  various  ruthenates 
with  special  supports  such  as  chromic  oxide  (Centralstelle  fur 
wissenschaftlich-technische  Untersuchungen) ,  and  sodamide 
with  different  promoters  as  manganese,  cobalt,  cerium,  etc., 
by  De  Jahn. 

It  is  important  to  avoid  certain  catalyst  poisons  such  as 
sulphur,  phosphorus,  arsenic,  lead,  tin,  oil,  impurities  carried 
mechanically  by  the  gases  from  steel  piping,  carbon  monoxide, 
etc.  Of  these  poisons  the  last  mentioned  is  not  the  least 
troublesome.  The  presence  of  small  quantities  of  sulphur 
in  the  iron  used  in  making  up  catalysts  is  sufficient  to  inhibit 
or  diminish  the  activity  while  it  is  necessary  to  free  the 
hydrogen,  usually  prepared  from  water  gas,  from  sulphur, 
carbon  monoxide,  etc.  The  removal  of  oxygen  and  water 
vapour  from  the  gases  is  also  desirable  in  most  cases. 

If  the  walls  of  the  vessels  containing  the  catalyst  are 
allowed  to  become  heated,  trouble  is  experienced  through  the 
action  of  the  hydrogen  on  the  steel  at  the  high  temperatures 
in  question,  namely,  500-700°  C.  Under  these  conditions 
the  carbon  of  the  steel  is  converted  into  methane  and  the 


HYDROGEN 

tensile  strength  of  the  steel  lowered  considerably.  The 
difficulty  may  be  minimized  by  the  use  of  special  steels  low 
in  carbon  and  containing  nickel,  chromium,  tungsten,  etc.,  as 
hardening  agents;  or  avoided  by  internal  electric  heating,  the 
pressure-resisting  walls  being  maintained  cold.  Other  special 
methods  of  preserving  the  steel  from  attack  have  been 
proposed  (cf.  B.P.s  20127/10,  1490/12,  8617/12,  28200/12, 
29260/12,  9661/14,  and  100216/16). 

It  is  specially  important  to  employ  efficient  heat-inter- 
changers  in  the  case  of  electric  heating,  the  problem  being 
comparatively  simple  when  dealing  with  compressed  gases  ; 
similarly  as  regards  the  separation  of  ammonia  by  cooling. 

In  order  to  guard  against  explosions  through  accidental 
admixture  of  oxygen  with  the  gases  (since  small  quantities, 
i.e.  more  than  5  %  (cf.  p.  203)  suffice  to  produce  explosive 
mixtures)  automatic  oxygen  detectors  are  preferably 
employed  (cf.  p.  34),  while  the  catalyst  containers  may  be 
disposed  in  bomb-proof  chambers. 

The  first  Badische  plant  was  erected  at  Oppau  in  1912  and 
produced  some  9000  tons  of  ammonia  per  annum,  a  lyinde- 
Frank-Caro  plant  of  capacity  about  70,000  ft.3/hr.  being 
installed  for  providing  the  necessary  hydrogen  ;  subsequently, 
and  particularly  during  the  war,  the  plant  has  been  greatly 
extended  and  at  the  present  time  the  production  is  probably 
of  the  order  of  100,000  tons  of  ammonia  per  annum.  Recently 
another  large  works  has  been  erected  at  Iveuna,  near 
Merseburg.  There  can  be  no  doubt  that  this  process 
played  a  large  part  in  providing  the  German  Army  with 
explosives  during  the  war. 

The  hydrogen,  the  cost  of  which,  in  the  requisite  high 
state  of  purity,  represents  a  large  fraction  of  the  whole, 
is  prepared  by  the  B.A.M.A.G.  continuous  catalytic  process 
(cf.  p.  161).  Except  in  special  cases  where  cheap  power  is 
available,  the  use  of  electrolytic  hydrogen,  so  eminently 
suitable  by  reason  of  its  purity,  is  out  of  the  question  in  view 
of  its  high  cost.  The  national  importance  of  the  fixation 
of  atmospheric  nitrogen,  involving  independence  of  overseas 
supplies  of  Chile  nitrate,  is  obvious,  ammonia  produced  by 


220  INDUSTRIAL   GASES 

direct  synthesis  being  specially  suitable,  on  account  of  its 
purity,  for  oxidation  to  nitric  acid.  The  Haber  process  has 
particular  advantages  for  this  country  as  the  power  consump- 
tion is  very  small  compared  with  the  requirements  of  other 
processes  for  nitrogen  fixation,  the  direct  arc  process,  the 
cyanamide  process,  etc.  (cf.  p.  117).  During  the  war  the 
importance  of  the  Haber  process  was  forced  into  general 
notice  among  the  Allied  Nations.  In  this  country  extensive 
investigations  have  been  carried  out  on  the  synthesis  of 
ammonia  (J.  Soc.  Chem.  Ind.,  (1917),  1196).  Similarly  in 
the  United  States  a  technical  process  has  been  developed 
by  the  General  Chemical  Co.  (cf.  Parsons,  J.  Ind.  Eng. 
Chem.,  (1917),  829  ;  also  B.P.  120546/18). 

It  is  unnecessary  to  dwell  on  the  uses  of  ammonia, 
usually  as  ammonium  sulphate,  for  fertilizing  purposes. 
One  objection  to  this  excellent  fertilizer,  as  compared  with 
other  sources  of  combined  nitrogen,  is  its  demand  for  sulphuric 
acid,  which  is  useless  except  for  the  purpose  of  fixing  the 
ammonia.  In  order  to  avoid  this  point,  many  patents  have 
been  taken  out  with  reference  to  the  use  of  gj^psum,  which  is 
caused  to  interact  with  ammonium  carbonate  (see  below), 
e.g.  B.P.  27962/13,  of  the  Badische  Co.,  which  relates  to  the 
troublesome  operation  of  filtering  the  resulting  calcium 
sulphate  and  of  washing  the  same  free  from  ammonium 
sulphate  by  means  of  immersion  filters  (cf .  Bosch,  Z.  Elektro- 
chem.,  24,  (1918),  361).  Other  recent  patents  of  the  Badische 
Co.  are  interesting  ;  they  relate  to  the  use  of  ammonium 
carbonate  as  a  fertilizer.  The  use  of  this  compound, 
containing  36  %  combined  nitrogen  as  compared  with  about 
20  %  in  ammonium  sulphate,  is  specially  important  in 
connection  with  the  manufacture  of  hydrogen  by  the 
continuous  catalytic  process,  which  produces  large  quantities 
of  carbon  dioxide  as  a  by-product.  For  an  interesting 
discussion  by  Matignon  of  the  validity  of  the  Badische  patents 
in  relation  to  certain  patents  by  Tellier,  the  Societe  Christi- 
ania  Minekompani,  etc.,  see  "  Comptes  Rendus  de  la  Seance 
d'Inauguration  des  travaux  de  la  Societe  de  Chimie  Industri- 
elle,"  p.  46  ;  Chem.  Trade  J.,  62,  (1918),  413. 


HYDROGEN  221 

Other  Applications  of  Hydrogen. — In  addition  to  the 
above  detailed  uses  hydrogen  has  been  used  extensively 
for  the  autogenous  fusion  of  metals,  the  flame  being  fed  with 
air  or  oxygen  ;  thus,  the  "  lead  burning  "  of  the  seams  of 
chemical  lead  work  is  often  conveniently  carried  out  with 
the  oxy -hydrogen  blowpipe,  similarly  with  the  welding  and 
cutting  of  iron.  The  use  of  the  more  conveniently  gener- 
ated acetylene  is,  however,  becoming  more  universal  and  has 
practically  displaced  that  of  hydrogen  for  such  purposes  (cf . 
"  Applications  of  Oxygen  ").  There  are  still  points  in  favour 
of  hydrogen  when  the  oxygen  is  generated  electrolytically  and 
the  hydrogen  is  a  waste  product.  The  oxy-hydrogen  blow- 
pipe is  used  for  the  fusion  of  platinum  in  lime  crucibles,  also 
for  the  working  of  fused  silica.  The  application  of  hydrogen  to 
the  manufacture  of  artificial  gems  was  initiated  by  Verneuil 
and  Paquiet  about  1900  and  later  developed  by  Wild, 
Miethe  and  L,ehmann.  Thus,  alumina  alone  gives  artificial 
corundum,  while  with  about  2j  %  chromic  oxide  rubies  are 
obtained,  similarly  sapphires  and  emeralds  may  be  produced, 
more  than  i  ton  of  gems  per  annum  being  thus  manufactured. 
Synthetic  rubies  are  valuable  for  small  bearings. 

Another  application  of  hydrogen  is  in  the  electric  lamp 
industry  ;  it  is  extensively  used  in  the  reduction  of  the 
tungsten  and  in  working  up  into  drawn  wire  filaments,  also 
for  the  filling  of  the  bulbs  before  evacuation,  usually  in  admix- 
ture with  about  an  equal  volume  of  nitrogen.  The  use 
of  hydrogen  for  aeronautical  purposes  is  dealt  with  in  the 
next  section. 

Hydrogen  at  a  pressure  of  120  atmospheres  and  costing 
about  \d.  per  ft.3  is  sold  in  cylinders  painted  red,  with  left- 
handed  connections. 

The  estimation  and  testing  of  hydrogen  are  discussed 
at  the  end  of  Section  VII. 

REFERENCES   TO    SECTION  VI. 

General. — Ellis,  "  The  Hydrogenation  of  Oils,  Catalysers  and  Catalysis, 
and  the  Generation  of  Hydrogen."  London,  1915. 

Brahmer,  "  Chemie  der  Gase."     Frankfurt  a. M.,  1911. 

Lepsius,  "  Sur  la  Fabrication  et  les  Applications  de  l'Hydrog£ne," 
Monit.  Scient.,  (1912),  493. 


222  INDUSTRIAL   GASES 

Sander,   "  Neuere  Verfahren  zur  Wasserstoffgewinnung,"   Z.  angew. 

Chem.,  (1912),  ii.,  2401. 
Blum,  "  New  Methods  of  Obtaining  Hydrogen,"  Metall.  and  Chem. 

Eng.,  (1911),  157- 
Crossley,    "  The   Preparation   and   Commercial   Uses  of   Hydrogen," 

/.  Soc.  Chem.  Ind.,  (1914),  1135. 
Linde-Frank-Caro    Process. — Linde,      "  Die     Wasserstoffgewinnung,"     Z. 

angew.  Chem.,  (1913),  iii.,  814. 
Linde,    "  Separation  'of  the   Constituents   of  Mixtures   of   Gases   by 

Liquefaction,"  /.  Soc.  Chem.  Ind.,  (1914),  714. 
Lane  and  Allied  Processes. — Barnitz,  "Production  of  Hydrogen  by  the 

Iron  Contact  Method,"  Chem.  Trade  J .,  60,  (1917),  547. 
Anon.,  "The  Generation  of  Hydrogen."  The  Engineer,  (1917),  546. 
Electrolytic     Hydrogen.— Engelhardt,      "The     Electrolysis     of     Water" 

(Richards).     Easton,  Pa.,  1904. 
Applications. — Frankland,  "  The  Chemical  Industry  of  Germany,"  /.  Soc. 

Chem.  Ind.,  (1915),  309. 
Hydrogenation   of  Oils  and  Fats. — Henderson,   "  Catalysis  in   Industrial 

Chemistry."     London,  1919. 

Maxted,  "  Catalytic  Hydrogenation  and  Reduction."     London,  1918. 
Ammonia  Synthesis. — Haber  and  Le  Rossignol,  "  Bestimmung  des  Am- 

moniakgleichgewichtes  unter  Druck,"   Z.  Elektrochem.,   14,   (1908), 

181  ;    "  Uber  die  technische  Darstellung  von  Ammoniak  aus  den 

Elementen,"  ib.,  19,  (1913),  53. 
Haber  in  collaboration  with  Tamaru,  Ponnaz,  Maschke,  Oehlom  and 

Greenwood,  Z.  Elektrochem.,  20,   (1914),  597;    21,  (1915),  87,  128, 

191,  206,  228,  241. 
Haber,  "  Die  Vereinigung  des  elementaren  Stickstoffs  mit  Sauerstoff 

und  mit  Wasserstoff,"  Z.  angew.  Chem.,  (1913),  iii.,  323. 
Bernthsen,  "  Synthetic  Ammonia,"  8th  Int.  Congress  of  A  pp.  Chem., 

N.Y.,  1912. 
Lunge,  "  Coal  Tar  and  Ammonia,"  Fifth  Edition,  Part  III.     London, 

1916. 
Norton,  "  Utilization  of  Atmospheric  Nitrogen,"  Dept.  of  Commerce 

and  Labour,  U.S.A.,  Special  Agents  Series,  No.  52. 
Partington,  "  The  Alkali  Industry."     This  Series.     1918. 


SECTION  VII.— THE  PRODUCTION  OF  HYDRO- 
GEN FOR  MILITARY  PURPOSES 

Field  Processes. — Of  late  years,  and  particularly  during 
the  war,  the  production  of  hydrogen  by  portable  or  semi- 
portable  plants  for  military  purposes  has  assumed  great 
importance.  In  the  early  days  of  ballooning  the  only  avail- 
able method  of  preparing  the  hydrogen  was  by  the  action 
of  sulphuric  acid  on  iron  or  zinc  which  process  had  the  great 
disadvantage  of  requiring  a  large  weight  of  material,  and 
although  of  comparatively  little  importance  with  the  small 
balloons  at  first  employed,  this  disadvantage  has  now 
rendered  the  method  quite  obsolete. 

The  first  use  of  methods  involving  less  weight  of  material 
was  in  the  Russo-Japanese  war  in  1904.  In  the  Soudan  war 
of  1885  and  also  in  the  Boer  war  of  1898-1902  hydrogen 
was  transported  from  England  in  cylinders.  Some  50 
horses  were  necessary  for  the  transport  of  the  cylinders 
required  for  a  balloon  of  14,000  ft.3  capacity.  It  is  interesting 
to  note  that  the  weight  of  the  steel  cylinders  is  of  the  order 
of  I  Ib.  per  ft.3  of  hydrogen  content.  Attention  was  conse- 
quently paid  to  methods  allowing  of  the  convenient  and 
rapid  generation  of  the  hydrogen  in  the  field. 

The  progress  of  the  large  dirigible  has  been  dependent 
on  the  advance  of  the  chemistry  of  hydrogen  production  and 
has,  in  turn,  served  as  a  stimulus  to  the  evolution  of  new 
processes.  Since  the  advent  of  the  Zeppelin  in  1898,  the 
capacity  of  balloons*  and  the  demand  for  hydrogen  in 
quantity  have  risen  steadily,  so  that  at  the  present  time 
the  various  types  of  military  hydrogen  plants  may  be  classified 
under  three  headings  : — 

(i)  Apparatus  of  a  simple  and  easily  portable  nature, 

*  British  rigid  dirigibles  having  a  capacity  of  2  to  3  million  it.3  have 
been  constructed  ;   German  Zeppelins  of  2  million  ft.*  capacity  were  used. 


224  INDUSTRIAL  GASES 

involving  a  small  weight  of  material  and  capable  of  giving 
rapid  generation  in  the  field,  the  cost  of  production  being 
of  secondary  importance  in  this  case. 

(2)  Apparatus  for  use  in  permanent  camps,  forts,  aviation 
depots,  etc.     Here,  again,  speed  of  erection  and  rapid  output 
may  be  of  more  importance  than  economy. 

(3)  Plant  suitable  for  economical  manufacture  on  a  large 
scale  with  a  view  to  subsequent  distribution  by  means  of 
cylinders. 

Portable  Apparatus  for  Use  in  the  Field 

Progress  in  this  direction  is  very  intimately  connected 
with  the  name  of  the  French  chemist,  Jaubert.  Some  of  the 
most  important  methods  are  the  following  : — 

Silicon  and  "Silicol ' '  Processes. — These  two  processes, 
which  have  been  extensively  adopted  for  military  purposes 
by  the  European  armies,  are  very  similar,  both  depending 
on  the  action  of  silicon  on  alkalis.  The  former,  however, 
uses  commercially  pure  silicon,  while  ferro-silicon  (rich  in 
silicon) ,  which  has  the  advantages  of  being  cheaper  and  more 
easily  produced,  is  employed  in  the  latter. 

Owing  to  hydrolytic  dissociation  of  the  sodium  silicate, 
less  caustic  soda  is  required  than  that  corresponding  to  the 
equation  : 

Si  +  2NaOH  +  H2O  =  Na2SiO3  +  2H2 

The  International  Chemical  Co.,  in  B.P.  14124/1900, 
claims  the  manufacture  of  hydrogen  by  treating  silicides  of 
the  alkaline  earths  with  water.  A  substance  Si2H2 — silico- 
acetylene — produced  by  treating  calcium  or  strontium 
silicide  with  acids,  gives  hydrogen  with  alkalis.  In  B.P. 
21032/09,  the  Consortium  fur  Elektrochemische  Industrie, 
G.m.b.H.  describes  the  production  of  hydrogen  by  the 
action  on  silicon  of  caustic  soda  solution  with  the  addition 
of  milk  of  lime,  less  caustic  soda  being  thus  required.  A  later 
patent,  B.P.  11640/11,  relates  to  the  attainment  without  an 
independent  boiler,  of  the  temperature  necessary  for  the 
reaction — (i)  by  a  preh'rninary  reaction  as,  for  example, 


HYDROGEN  FOR  MILITARY  PURPOSES    225 

the  solution  of  aluminium  in  the  caustic  soda,  and  (2)  by 
adding  the  alkali  to  the  water  in  the  form  of  powdered  sodium 
hydroxide  or  oxide.  A  further  series  of  patents  is  due  to 
J aubert,  who  employs  f erro-silicon  instead  of  silicon.  Accord- 
ing to  B.P.  17589/11  (cf.  also  F.P.  430302/10),  ferro-silicon,  or 
mangano-silicon,  is  treated  with  a  concentrated  solution  of 
potassium  sulphate  or  sodium  sulphate  containing  alkali. 
The  salts  serve  to  raise  the  boiling  point  and  so  increase 
the  reaction  velocity.  The  same  object  is  attained  in  F.P. 
433400/10  by  the  use  of  increased  pressure.  In  B.P. 
7494/13  is  prescribed  the  use  of  a  layer  of  unsaponifiable 
oil  facilitating  the  admixture  of  the  ferro-silicon  with  the 
caustic  soda  solution  and  ensuring  very  rapid  generation 
of  gas  ;  water  is  added  to  replace  that  lost.  Baillio,  in  U.S. P. 
1178205/16,  combines  the  production  of  hydrogen  with  that 
of  sodium  silicate  from  silicon  and  caustic  soda,  the  former 
being  used  in  excess. 

TheSchuckert  Process. — The  Schuckert  process  depends  on 
the  use  of  silicon  itself  and  has  been  developed  mainly  in 
Germany,  as  a  portable  field  apparatus.  A  temperature  of 
80-90°  C.  is  required  for  the  rapid  progress  of  the  reaction 
and  the  heat  of  solution  of  the  caustic  soda  is  utilized  by 
building  the  dissolver  into  the  generator.  A  feed  hopper 
is  provided  for  the  gradual  introduction  of  the  finely  divided 
silicon,  and  the  hydrogen  passes  off  through  a  washer  fed 
with  water  by  a  pump  driven  by  a  petrol  engine.  Plants  of 
this  type  have  been  constructed  with  a  capacity  of  2000- 
4000  ft.3/hr. 

The  apparatus  was  first  used  by  the  Spanish  in  the 
Moroccan  campaign,  and  was  also  used  by  the  Italians  in 
Tripoli.  Stationary  plants,  with  a  capacity  of  10,000  ft.3/hr., 
have  been  set  up.  The  caustic  soda  solution  employed  is 
of  20-25  %  concentration ;  each  1000  ft.3  of  hydrogen 
requires  50  Ibs.  of  silicon,  75  Ibs.  of  caustic  soda,  and  about 
190  gallons  of  water,  inclusive  of  cooling  water. 

The  Silicol  Process. — This  process,   due  to  the  French 
chemist  J  aubert,  has  been  largely  used  by  the  French  military 
authorities.     Instead  of  silicon,   the   cheaper  ferro-silicon, 
A.  15 


226  INDUSTRIAL   GASES 

containing  90  %  or  more  silicon,  is  employed.  Using  a 
35~4°  %  caustic  soda  solution,  the  action  takes  place  ener- 
getically at  60-80°  C.  ;  the  concentrated  solution  has  the 
effect  of  conserving  the  heat  of  reaction  by  minimizing 
vaporization  of  water,  while  the  initial  temperature  required 
for  the  reaction  is  easily  attained  in  dissolving  up  the  caustic 
soda,  no  external  heating  being  necessary. 

Portable  plants,  with  an  hourly  output  of  14,000  ft.3, 
have  been  built ;  the  usual  pattern,  however,  has  a  capacity 
of  about  2500  ft.3/hr.  and  is  mounted  on  a  3-ton  lorry. 
The  general  arrangement  of  the  apparatus  is  almost  the  same 
as  in  the  Schuckert  plant. 

I^arge  stationary  plants  on  these  lines  have  been  erected 
for  the  British  Navy  at  Chatham  and  elsewhere  during  the 
war,  by  the  Societe  Fran9aise  1'Oxy lithe.  The  plant  at 
Chatham  has  a  capacity  of  some  50,000  ft.3/hr.  The  caustic 
soda,  broken  into  small  pieces,  is  stirred  with  i|  times  to 
twice  its  weight  of  water  in  a  dissolver,  whereby  a  temper- 
ature of  60-80°  C.  is  reached  ;  the  solution  is  then  run  into 
the  generator.  By  means  of  a  mechanically-operated  distri- 
butor, the  finely  powdered  ferro-silicon  is  fed  into  the  gener- 
ator which  is  provided  with  a  planetary  stirrer.  A  slow 
stream  of  paraffin  or  naphtha  is  also  admitted  to  prevent 
the  formation  of  foam  which  would  hinder  the  progress  of  the 
reaction.  The  hydrogen  is  cooled  and  purified  by  passage 
through  a  scrubber  fed  with  water  and  containing  metal 
spirals,  and  then  freed  from  suspended  water  by  traversing, 
at  high  speed,  a  series  of  tubes  with  abrupt  changes  of 
direction.  Two  generators  are  provided,  one  serving  as  a 
standby. 

It  is  obvious  that  the  hydrogen  produced  in  this  type 
of  stationary  plant  is  very  expensive  compared  with  that 
from  other  processes.  The  very  high  speed  of  gas  generation 
in  case  of  necessity  is,  however,  an  important  consideration 
for  war  purposes. 

These  two  processes  have  some  disadvantages.  On  account 
of  the  vigorous  heat  evolution  a  considerable  amount  of 
fairly  clean  water  is  required,  while  the  hydrogen  is  liable 


HYDROGEN  FOR  MILITARY  PURPOSES     227 

to  contain  small  amounts  of  phosphine  (according  to  Soyer, 
Ann.  Chim.Analyt.,  23,  (1918),  221,  some  0*0025  to  0-007  % 
by  volume  may  be  present),  arsine,  sulphuretted  hydrogen, 
etc.,  derived  from  impurities  in  the  ferro-silicon  and  having 
an  injurious  effect  on  the  balloon  fabrics.  For  data  on  the 
production  of  ferro-silicon,  cf.  Anderson, '/.  Soc.  Chem.  Ind.t 

(1917),  881. 

Hydrogenite  Process. — This  process,  also  due  to  M. 
Jaubert  (cf.  Rev.  Gen.  Chim.,  13,  341,  357),  resembles  the 
silicol  process  in  depending  on  the  action  of  alkalis  on  ferro- 
silicon,  but  differs  in  that  the  reaction  is  carried  out  in  the 
absence  of  water  and  at  a  high  temperature. 

The  basis  of  all  the  patents  given  below  is  the  preparation 
of  mixtures  which  react  by  auto-combustion  in  absence  of 
air  when  the  action  is  started  by  local  heating,  hydrogen 
being  evolved.  Similar  mixtures  are  used  for  oxygen  produc- 
tion (q.v.).  Jaubert,  in  B.P.  17252/07,  describes  apparatus 
for  the  generation  of  hydrogen  under  pressure  by  the  auto- 
combustion  method.  The  actual  generator  is  surrounded  by 
and  is  in  direct  connection  with  the  gas  reservoir,  the  pressure 
being  thus  balanced  inside  and  outside.  The  same  inventor, 
in  B.P.  153/11,  deals  with  the  production  of  hydrogen  by  the 
interaction  of  ferro-silicon,  lime  and  caustic  soda  in  a  closed 
vessel,  the  reaction  being  first  started  by  local  heating, 
According  to  a  later  patent,  B.P.  9623/11,  excess  ferro- 
silicon  is  mixed  with  an  oxidizing  agent  and  a  hydrate.  As 
examples  of  suitable  combinations  are  given — (i)  powdered 
iron  20  parts,  soda-lime  10  parts,  potassium  perchlorate  6 
parts  ;  (2)  ferro-silicon  (75  %  silicon)  20  parts,  litharge  10 
parts,  soda-lime  (two-thirds  caustic  soda)  60  parts  ;  (3)  ferro- 
silicon  20  parts,  powdered  iron  5  parts,  wheaten  flour  3 
parts,  lime  5  parts,  potassium  chlorate  3  parts.  The  reaction 
may  also  be  effected  by  steam  produced  in  an  annular  boiler 
round  the  generator.  According  to  B.P.  5005/12,  the  oxi- 
dation of  the  ferro-silicon  is  effected  solely  by  the  steam 
generated  as  above,  no  other  oxidizing  agent  being 
employed. 

"  Hydrogenite  "  consists  of  an  intimate  mixture  of  25 


228  INDUSTRIAL   GASES 

parts  of  ferro-silicon  (90-95  %  silicon),  60  parts  of  caustic 
soda  and  20  parts  of  soda-lime.  The  gray  compressible 
powder  thus  obtained  is  pressed  into  blocks  which  are  packed 
in  air-tight  cases  holding  from  J  to  i  cwt.  ;  under  these 
conditions  the  mixture  is  quite  permanent.  When  required 
for  use  the  lid  is  removed,  the  box  placed  in  the  generator, 
and  the  heavy  lid  of  the  latter,  kept  in  position  by  its  weight 
alone  and  serving  as  a  safety  valve,  is  put  on.  The  mass 
is  then  ignited  through  a  small  hole  in  the  lid  by  means  of 
a  match  applied  to  a  small  quantity  of  priming  powder, 
when  the  reaction  propagates  itself  throughout  the  mass, 
without  production  of  flame,  hydrogen  being  produced  very 
rapidly.  The  generator  is  surrounded  by  a  water  jacket  in 
which  steam  is  generated.  Towards  the  end  of  the  reaction 
this  steam  is  admitted  to  the  generator,  serving  to  increase 
the  yield  and  to  quench  the  mass.  The  hydrogen  is  washed 
with  water  and  dried  with  coke  and  sawdust. 

Portable  plants  have  been  used  by  the  French  Army, 
consisting  of  waggons  with  6  generators  grouped  round  a 
central  washer ;  the  capacity  is  about  5000  ft.3  hydrogen 
per  hour.  The  method  has  the  important  advantage  over 
other  processes  of  requiring  no  water,  and  further,  of  using 
the  same  material  as  the  important  silicol  process.  Each 
1000  ft.3  of  hydrogen  necessitates  a  weight  of  about  190  Ibs. 
of  hydrogenite.  The  gas  obtained  is  very  pure. 

Hydrolith  Process. — Jaubert,  in  F.P.  327878/02,  deals 
with  the  preparation  of  calcium  hydride  from  calcium 
and  waste  hydrogen,  e.g.  from  electrolytic  alkali  manufacture. 
The  hydrogen,  freed  from  water  and  oxygen,  is  passed  over 
calcium  heated  to  about  600°  C.  A  later  patent,  B.P. 
25215/07,  describes  an  apparatus  for  producing  hydrogen 
from  calcium  hydride,  consisting  of  a  series  of  generators  so 
arranged  that  the  moisture  from  one  generator  is  removed  by 
passing  the  gas  through  another  generator  filled  with  cal- 
cium hydride  but  not  supplied  with  water.  A  modified 
process  is  described  in  D.R.P.  218257/08,  by  Bamberger, 
Bock  and  Wanz,  who  use,  instead  of  water,  substances 
containing  combined  water  or  carbon  dioxide,  e.g.  gypsum, 


HYDROGEN  FOR    MILITARY  PURPOSES    229 

sodium  bicarbonate,  etc.,  which  only  react  when  heated  to  a 
temperature  above  80°  C. 

Hydrolith  reacts  with  water  as  follows : — 

CaH2  +  2H2O  =  Ca(OH)2  +  2H2 

The  calcium  hydride  is  prepared  by  treating  molten  calcium 
with  hydrogen  and  serves  as  a  medium  for  transporting 
waste  hydrogen  to  the  balloons ;  although  expensive, 
its  use  avoids  the  great  weight  of  cylinders.  A  white 
crystalline  powder,  consisting  of  90  %  calcium  hydride  with 
some  nitride  and  oxide,  is  obtained,  and  on  treatment  with 
cold  water,  1000  ft.3  of  hydrogen  are  produced  from  the 
exceptionally  small  weight  of  62  Ibs.  A  waggon,  carrying 
6  generators,  yields  some  15,000  ft.3/hr.,  while  plants  with  a 
capacity  of  50,000  ft.3/hr.  have  been  constructed.  Such  a 
plant  with  a  supply  of  20  tons  of  calcium  hydride,  i.e.  capable 
of  producing  700,000  ft.3  hydrogen,  was  used  in  recent 
French  manoeuvres  and  behaved  very  well.  The  generators, 
carrying  the  calcium  hydride  on  perforated  plates,  are 
supplied  with  water  at  the  bottom  while  the  hydrogen 
passes  off  at  the  top  and  is  freed  from  water  by  passing 
through  another  generator  containing  an  untreated  charge 
which  is  subsequently  used.  A  large  heat  evolution  takes 
place,  which  at  first  caused  inconvenience.  The  hydrogen 
leaving  the  generators  is  purified  from  a  small  quantity  of 
ammonia  before  use. 

By  the  Action  of  Acids  and  Alkalis  on  Metals. — 
This  branch  of  the  subject  may  be  divided  into  several 
sections  : — 

(i)  Action  of  Sulphuric  Acid  on  Iron  or  Zinc. — In  this 
connection  there  are  a  large  number  of  patents,  among  which 
may  be  mentioned  the  following  :  Pratis  and  Marengo,  in 
B.P.s  16277/96  and  15509/97,  describe  apparatus  for  the 
generation  of  hydrogen  from  sulphuric  acid  and  iron  (cf .  also 
Hawkins,  B.P.  25,084/97 ;  Fielding,  B.P.  17516/98,  and 
Praceiq  and  Bourchaud,  B.P.  6075/05). 

The  use  of  such  methods  for  generating  hydrogen  is  very 
old,  and  although  convenient  for  relatively  small  quantities 


230  INDUSTRIAL  GASES 

on  a  large  laboratory  scale,  for  lead  burning  and  allied  pur- 
poses,* is  too  expensive  and  involves  too  great  weight  of 
material  for  military  purposes  (cf.  p.  234)  ;  consequently  for 
field  work  these  methods  have  been  abandoned  (cf.  also 
p.  223). 

A  considerable  amount  of  work  was  carried  out  by  Renard 
(1875-1880)  in  the  development  of  this  process  for  military 
purposes  in  France.  Acid  of  some  12  %  strength  was  run 
on  to  iron  or  zinc  in  a  leaden  vessel ;  the  hydrogen  was 
washed  with  water,  freed  from  sulphuretted  hydrogen  with 
Ivaming's  mixture  (quicklime,  ferrous  sulphate  and  sawdust) 
and  then  passed  over  caustic  soda,  the  plant  yielding  some 
1000  ft.3  hydrogen  per  hour.  Hydrogen  generated  from  iron 
or  zinc  is  liable  to  have  a  low  lifting  power  on  account  of 
impurities  and  to  contain  sulphuretted  hydrogen  and,  when 
using  zinc,  arsine  ;  these  impurities  have  an  injurious  action 
on  the  balloon  fabrics,  while  the  arsine  is  further  objectionable 
by  reason  of  its  poisonous  properties.  Attempts  have  been 
made  to  remove  arsenic  from  the  hydrogen  by  passing  through 
a  heated  tube  containing  copper  turnings  ;  by  the  action 
of  potassium  permanganate  ;  cooling  with  liquid  air,  etc. 
(cf.  p.  21 1).  Arsenic- free  acid  should,  of  course,  be  used  in 
the  preparation. 

(2)  Action  of  Caustic  Soda  on  Aluminium. — This  method 
has  long  been  known,  but  only  recently  used  for  military 
purposes.  It  was  employed  by  the  Russians  in  the  Russo- 
Japanese  war  in  1904,  two  types  of  portable  apparatus 
being  employed  : — (i)  Two  generators  with  a  common  washer 
mounted  on  two  cars,  the  set  having  a  capacity  of  5000 
ft.3/hr.  (2)  Two  generators  of  light  pattern  carried  by 
a  pack-horse  for  use  in  mountainous  country.  The  sheet- 
iron  generators  were  filled  with  30  %  caustic  soda  solution 
in  the  lower  part  and  a  basket  containing  aluminium  sheet 
clippings  was  lowered  by  means  of  a  handle.  The  hydrogen 
was  washed  in  a  water  scrubber.  A  very  vigorous  reaction 
takes  place  and  an  ample  supply  of  cooling  water  is  necessary. 

*  For  useful  data  on  the  preparation  and  compression  of  hydrogen  on 
a  large  laboratory  scale,  cf.  Hutton  and  Petavel,  loc.  cit.,  p.  113. 


HYDROGEN  FOR  MILITARY  PURPOSES    231 

Reference  to  Table  25  will  show  that  the  weight  of  material 
is  still  rather  high  although  less  than  that  required  when 
using  iron  or  zinc  with  sulphuric  acid. 

(3)  Action  of  Activated  Aluminium  on  Water. — Considerable 
attention  has  been  paid  to  the  activation  of  aluminium 
with  mercury  to  ensure  rapid  evolution  of  hydrogen  on 
treatment  with  water  alone.  A  great  advantage  is  the  small 
weight  of  material  requiring  transport.  Thus,  Mauricheau- 
Beaupre,  in  F.P.  392725/08,  generates  hydrogen  by  the  slow 
addition  of  water  to  a  mixture  of  fine  aluminium  filings  with 
1-2  %  of  mercuric  chloride  and  0-5-1  %  of  potassium 
cyanide,  the  temperature  being  kept  below  70°  C.  One  gallon 
of  water  suffices  for  10  Ibs.  of  the  material,  which  has  a  specific 
gravity  of  1*4  and  is  permanent  in  absence  of  air  and  moisture. 
Similarly  the  Chemische  Fabrik  Griesheim-Blektron,  in  B.P. 
3188/09,  uses  a  mixture  of  finely  divided  aluminium  with 
i  %  mercuric  oxide  and  i  %  caustic  soda.  This  mixture 
has  the  advantage  of  being  less  poisonous  than  the  above. 
A  patent  by  Sarason,  B.P.  18772/11,  prescribes  the  addition 
of  a  salt  having  an  alkaline  reaction,  e.g.  a  borate,  phosphate, 
etc.,  to  start  the  action  of  the  water  on  the  aluminium 
amalgam.  Uyeno  (B.P.  11838/12)  treats  an  alloy  of  aluminium 
and  zinc  which  may  also  contain  tin,  with  zinc  or  tin  amalgam 
and  subsequently  heats  to  cause  penetration  of  the  mercury. 
The  product  yields  'hydrogen  on  treatment  with  hot  water 
(cf.  also  D.R.P.  294910/16  by  Blkan  Krben,  G.m.b.H.). 

Other  Processes. — A  series  of  patents  deals  with  the 
employment  of  metallic  sodium,  avoiding  the  usual  violent  re- 
action. Thus,  Foersterling  and  Philipp,  in  U.S.P.  883531/08, 
propose  to  treat  sodium  in  small  pieces  with  a  spray  of  water 
at  such  a  rate  that  no  solution  is  formed,  while,  according  to 
U.S.P.  977442/10,  sodium  is  kneaded  with  aluminium 
silicide  and  briquetted.  The  resulting  product  gives  hydrogen 
on  treatment  with  water  ;  cf .  also  Philipp,  U.S.P.  1041865/12. 
In  like  manner  Brindley,  in  U.S.P.  909536/09,  briquettes  an 
intimate  mixture  of  sodium  with  crude  oil,  kieselguhr  and 
also  aluminium  or  silicon,  the  mass  being  subsequently 
treated  with  water.  For  a  proposal  to  use  lead-magnesium 


232  INDUSTRIAL  GASES 

and  similar  alloys,  cf.  Ashcroft,  Trans.  Faraday  Soc.,  (1918), 
July  23.  A  lead-sodium  alloy  known  as  "  hy drone,"  yielding 
hydrogen  on  treatment  with  water,  has  also  been  proposed. 
Another  field  method  based  on  experiments  described  by 
Schwarz  (Ber.,  19,  (1886),  1140)  has  been  developed  by 
Majert  and  Richter,  and  depends  on  the  interaction  of  a 
heated  mixture  of  soda-lime  and  zinc  dust : 

Zn  +  Ca(OH)2  =  ZnO  +  CaO  +  H2 

The  mixture  is  disposed  in  a  series  of  horizontal  tubes  mounted 
in  a  heating  chamber.  The  use  of  a  mixture  of  glycerol  and 
caustic  soda  has  been  proposed.  The  process  is  convenient, 
but  is  rather  dangerous. 

Adaptations  of  Stationary  Types  of  Plant  to  Field 

Purposes 

By  mounting  on  railway  trucks  it  has  been  found  possible 
to  use  some  of  the  less  portable  types  of  plant  for  field 
purposes  as,  e.g.  the  Rincker  and  Wolter  process  (cf.  p.  192), 
plants  with  a  capacity  of  3500  ft.3  hydrogen  per  hour  being 
thus  constructed.  The  process  gives  cheap  hydrogen,  but 
the  lifting  power  is  not  very  high  on  account  of  the  nitrogen 
and  carbon  monoxide  contents  (see  p.  193). 

Semi-Portable  Plant 

Certain  of  the  processes  described  under  (i)  have  been 
adopted  for  use  in  air  stations,  etc.,  although  the  expense  is 
rather  unwarrantable  in  such  cases.  Many  air  stations  have 
been  equipped  with  electrolytic  plants  (cf.  194).  Thus  an 
Oerlikon  plant  was  installed  at  the  Farnborough  air  station  ; 
plants  have  also  been  put  down  by  various  European  powers, 
while  the  U.S.  Army  had  an  electrolytic  plant  of  capacity 
3000  ft.3/hr. 

In  such  cases,  the  stations  are  equipped  with  compression 
plants  and  with  cylinders  for  purposes  of  distribution.  The 
French  Army  has  used  very  large  cylinders,  namely,  13  ft. 
long  and  io|  in.  internal  diameter,  with  capacity  at  130 
atmospheres  of  about  900  ft.3.  In  Germany,  special  railway 


HYDROGEN  FOR  MILITARY  PURPOSES    233 

waggons  have  been  used,  each  carrying  500  cylinders,  all 
inter-connected  by  soldered  joints  to  a  single  discharge 
valve.  Each  waggon  weighs  about  30  tons  and  carries 
nearly  100,000  ft.3  of  hydrogen,  some  8  such  waggons  being 
required  for  a  dirigible  of  volume  700,000  ft.3. 

Stationary  Plants 

In  this  category  may  be  included  practically  all  the 
processes  described  in  Section  VI.  The  hydrogen  may  be 
distributed  in  cylinders  as  described  above.  Utilization  of 
waste  electrolytic  hydrogen  has  already  been  mentioned  ; 
the  gas  may  be  piped  directly  to  the  aerodrome  or  may  be 
distributed  in  cylinders.  On  account  of  the  much  greater 
economy  of  production  possible  by  such  methods,  hydrogen 
can  be  so  made  for  aeronautical  purposes  in  large  quantities 
with  advantage,  provided  that  the  freight  costs  are  not  too 
great.  The  lyinde-Frank-Caro  has  the  advantage  with 
regard  to  aviation,  that  it  is  adaptable  to  the  recovery  of 
the  hydrogen  in  spent  balloon  gas,  i.e.  hydrogen  which  has 
to  be  discarded  by  reason  of  its  diminished  lifting  power  on 
account  of  the  diffusion  through  the  fabric  of  a  considerable 
quantity  of  air,  e.g.  25  %. 

General. — There  are  three  important  considerations 
relating  to  the  manufacture  of  hydrogen  for  balloons — 
(i)  lifting  power  as  determined  by  purity  ;  (2)  effect  on  the 
fabric;  (3)  cost. 

(i)  Lifting  Power  of  the  Hydrogen. — Since  1000  ft.3  of 
pure  hydrogen  at  15°  C.  weigh  5*319  Ibs.  and  1000  ft.3  of  dry 
air  at  15°  C.  weigh  76-49  Ibs.,  it  follows  that  the  lifting 
power  of  pure  hydrogen  at  15°  C. 

=  76-49  —  5-32  Ibs./iooo  ft.3 
=  71*17  Ibs./iooo  ft.3 

A.  simple  calculation  will  show  that  the  presence  of  i  % 
of  air  derived  by  diffusion  through  the  envelope,  would  lower 
the  lifting  power  by  exactly  i  %,  while  the  presence  of  the 
water  vapour  corresponding  to  15°  C.  would  have  a  like 
effect.  The  influence  of  the  saturation  of  the  air  is  obviously 


234 


INDUSTRIAL  GASES 


small,  saturation  at  15°  C.,  for  instance,  only  reducing  the 
lifting  power  by  07  %. 

(2)  Effect  on  Fabrics. — It  has  been  found  that  sulphuretted 
hydrogen,   arsine  and  phosphine  have  an  injurious  eifect 
on  the   balloon  fabric,  probably  due  to  oxidation  of   the 
impurities  to  sulphuric,  arsenic  and  phosphoric  acids    re- 
spectively.    Electrolytic  hydrogen  has  an  advantage  from 
this  point  of  view  over  that  produced  by  other  methods. 

(3)  Costs. — The  following  table  shows  the  relative  costs, 
as  far  as  data  are  available,  of  various  field  methods  for 
making   hydrogen,  together  with  the  weights  of   material 
(water  excluded)  required  per  1000  ft.3  of  hydrogen.     The 
costs  must  be  considered  as  approximations  only  and  in 
any  case  refer  to  pre-war  conditions. 

TABLE   25. 

COST  OF  PRODUCTION  OF  HYDROGEN  AND  WEIGHT  OF  MATERIALS 
REQUIRED  BY  DIFFERENT  FlELD  PROCESSES. 


Process. 

Cost  per  1000  ft.3 
Shillings. 

Material  required 
per  1000  ft." 

Lbs. 

Silicon  (Schuckert)  process 

20 

125 

Silicol  (Jaubert)  process 

20 

120 

Hydrogenite  process 

40 

IQO 

Hydrolith  process 

7° 

60 

Iron  and  sulphuric  acid 

15-25 

450-500 

Zinc  and  sulphuric  acid 

40 

450-500 

(with  O.  V.  (80  %) 

at  255.  per  ton) 

Aluminium  and  caustic  soda  .  .          .  . 

70 

350 

Activated  aluminium  and  water: 

Mauricheau-Beaupre  process 

50 

5° 

Griesheim-Elektron  process 

5° 

60 

Before  leaving  the  subject  of  balloons,  it  is  interesting 
to  note  that  proposals  have  been  made  to  substitute  helium 
for  hydrogen  on  account  of  the  non-inflammability  of  the 
former  in  conjunction  with  its  high  lifting  power. 

Thus,  the  weight  of  1000  ft.3  of    air     at  15°  C.  =  76-49  Ibs. 
,,  ,,  ,,  helium        ,,        =  10-56  Ibs. 

Consequently  the  lifting  power  of  1000  ft.3  of 

helium  at  15°  C =  65-93  Ibs. 

or  92  %  of  that  of  hydrogen. 


HYDROGEN  FOR  MILITARY  PURPOSES    235 

Estimation  and  Testing  of  Hydrogen.— Hydrogen  is 
not  readily  estimated  in  gaseous  mixtures  by  simple 
absorption,  although,  if  desired,  absorption  can  be  effected 
by  means  of  metallic  palladium,  by  chlorate  solutions  in  the 
presence  of  colloidal  osmium  or  by  other  allied  methods  (cf . 
the  work  of  Paal,  Hofmann  and  others,  p.  155). 

In  general,  hydrogen  is  usually  estimated  by  combustion 
with  excess  oxygen  ;  this  operation  may  be  effected  in  various 
ways,  e.g.  by  explosion,  in  a  Grisoumeter  or  over  palladized 
asbestos,  or  copper  oxide  may  be  used  without  addition  of 
oxygen.  When  hydrogen  and  methane  occur  together, 
fractional  combustion  can  be  effected  quite  cleanly  by 
attention  to  temperature,  both  with  palladized  asbestos  and 
copper  oxide. 

Turning  to  the  examination  of  commercial  hydrogen, 
the  purity  can  be  readily  determined  to  a  first  approximation 
by  means  of  physical  methods,  e.g.  by  effusion.     Impurities, 
such  as  carbon  monoxide,  carbon  dioxide  and  oxygen,  are 
easily  estimated  by  methods  described  under  these  gases, 
while  reference  has  been  already  made  to  the  automatic 
detection  of  oxygen  in  electrolytic  hydrogen,  etc.     Nitrogen 
is  best  determined  by  combustion  with  copper  oxide  and 
measurement    of    the    residue.      Hydrogen    made   by    the 
B.A.M.A.G.  continuous  catalytic  process  contains  methane 
which,  in  view  of  the  small  quantit}^  present,  is  best  esti- 
mated by  complete  combustion  of  a  stream  of  the  hydrogen 
with  excess  oxygen  and  determination  of  the  resulting  carbon 
dioxide,  due  allowance  being  made  for  any  carbon  monoxide 
present.     Alternatively  the  estimation  may  be  performed  by 
explosion  and  subsequent  measurement  of  the  carbon  dioxide 
formed.    The  Silicol  process  gives  hydrogen  containing  traces 
of  phosphine  ;  according  to  Soyer  (loc.  cit.,  p.  227)  the  pro- 
ducts of  combustion  of  from  2-20  litres  of  the  hydrogen  are 
taken  up  with  water  and  phosphoric  acid  estimated  as  phos- 
phomolybdic  acid.     Arsenic  may  be  estimated  by  the  usual 
method  of  passing  the  gas  through  a  heated  glass  capillary 
and  comparing  the  mirror  with  standards,  or  by  the  Gutzeit 
method  depending  on  the  production  of  a  brown  or  yellow 


236  INDUSTRIAL  GASES 

stain  on  mercuric  chloride  paper.  Sulphuretted  Irydrogen 
and  carbon  disulphide  may  occur  in  hydrogen  ;  the  former 
may  be  estimated  by  its  action  on  lead  acetate  paper  or  on 
iodine  solution,  etc.,  while  the  latter  may  be  similarly  deter- 
mined after  its  conversion  into  sulphuretted  hydrogen  by- 
passing over  platinized  pumice  at  300-350°  C. 


REFERENCES  TO  SECTION  VII. 

Sander,  "  Zur  Geschichte  der  Wasserstoffgewinnung  im  Kriege,"  /. 
Gasbeleucht,  58,  (1915),  637. 

Anon.,  "  Hydrogen  for  Balloons,"  Engineering,  99,  (1915),  415. 

Boyer,  "  La  Nouvelle  Usine  a  1'Hydrog^ne  de  1'Arsenal  de  Chatham," 
La  Nature,  (1915),  i.  144. 

Fourniols,  "  La  Fabrication  de  1'Hydrogene  pour  le  Gonflement  des 
Ballons,"  Rev.  Gen.  des  Sciences,  26,  (1915),  339. 


SECTION  VIII.— CARBON  MONOXIDE 


Properties  of  Carbon  Monoxide. — Carbon  monoxide  is 
a  colourless  gas  which,  according  to  Merriman,  has  a  definite 
metallic  odour  and  taste.  The  chief  physical  properties 
will  be  found  in  Tables  12  and  13,  pp.  53-56.  The  solubility 
in  water  is  given  by  the  following  table  :  — 


Temperature  °C  

o 

10 

15 

20 

40 

C.c.  of   gas,  measured  at 

N.T.P.,     dissolved     by 

i  c.c.  of  water  under  a 

pressure  of  I  atm.  ex- 

clusive of  water  vapour 

0-035 

0-028 

0-025 

0-023 

o'oiS 

Carbon  monoxide  is  readily  formed  by  the  combustion 
of  carbon  in  a  limited  supply  of  oxygen  and  by  a  number 
of  chemical  reactions.  The  most  important  commercial 
form  of  carbon  monoxide  is  in  admixture  with  nitrogen, 
hydrogen,  etc.,  in  producer  gas,  water  gas  and  the  like. 

Carbon  monoxide  is  a  poisonous  gas,  forming  a  compound 
with  the  haemoglobin  of  the  blood  (carboxy haemoglobin), 
and  is  only  very  slowly  replaced  by  the  normal  oxygen.  A 
concentration  of  0-4  %  is  rapidly  fatal.  Carbon  monoxide 
burns  with  a  characteristic  blue  flame  to  carbon  dioxide.  It 
is  very  stable  at  high  temperatures,  especially  in  the  presence 
of  a  trace  of  moisture  (Woltereck,  Comptes  Rend.,  147,  (1908), 
460),  but  in  the  neighbourhood  of  300°  C.  and  in  the  presence 
of  a  catalyst,  e.g.  metallic  nickel,  decomposition  takes  place 
according  to  the  following  equation  :  — 

2CO  -F^  CO2  +  39,300  calories. 

The  following  table  gives  the  percentages  of  carbon 
dioxide  in  equilibrium  with  carbon  monoxide  and  carbon 
at  different  temperatures  and  at  atmospheric  pressure.  The 


238 


INDUSTRIAL   GASES 


values  above  850°  C.  are  taken  from  Rhead  and  Wheeler 
(Chem.  Soc.  Trans.,  (1910),  2178  ;  (1911),  1141)  and  the 
lower  values  from  Boudouard  (Annales  de  Chimie  et  de  Phys., 
[7],  24,  (1901),  5). 

TABLE   26. — EQUILIBRIUM  BETWEEN  CARBON 


Temperature  °C  

450 

500 

600 

700 

Percentage  CO21  B. 
by  volume      /R.  and  W. 

98 

95    - 

77 

42 

foo2 
pco 

49-0 

19-0 

3'  35 

0-724 

K 


2450 


380 


1 4' 55 


1-25 


Rhead  and  Wheeler  adopt  the   modified  L,e   Chatelier 
formula  given  below  as  in  agreement  with  their  measurements. 


log 


=  1874  -  log,P  - 


38,055  +  2'02T 


In  view  of  the  decrease  in  volume  as  decomposition 
proceeds,  it  is  obvious  that  the  effect  of  increased  pressure 
will  be  to  favour  such  decomposition.  Experiments  by 
Briner  and  Wroczynski  (Comptes  Rend.,  150,  (1910),  1324) 
have  demonstrated  that  at  400  atmospheres  carbon  monoxide 
is  not  decomposed  at  the  ordinary  temperature  even  in  the 
presence  of  platinized  asbestos ;  at  320-360°  C.  slow 
decomposition  occurred,  a  diminution  in  volume  of  10  % 
being  observed  after  20  hours. 

Carbon  monoxide  reacts  with  water  vapour  at  quite  low 
temperatures,  e.g.  400°  C.,  in  the  presence  of  a  suitable 
catalyst,  giving  the  so-called  water  gas  equilibrium — 

CO  +  H2O  ^  CO2  +  H2  +  10,200  calories. 

This  equilibrium  is  dealt  with  elsewhere,  see  pp.  157  and  309. 
The  equilibrium  constant  becomes  unity  at  a  temperature  of 
about  830°  C.;  which  means  that  below  this  temperature 


CARBON  MONOXIDE 


239 


carbon  monoxide  is  a  more  active  reducing  agent  than 
hydrogen  and  above  this  temperature  less  so.  Thus,  it  is 
found  that  carbon  monoxide  begins  to  reduce  metallic  oxides 
at  a  considerably  lower  temperature  than  does  hydrogen, 

MONOXIDE,   CARBON  DIOXIDE  AND  CARBON. 


800 

900 

IOOO 

IIOO 

I2OO 

7 

2'22 

0'59 

0-15 

0'06 

0-0752 

O-O227 

O-OOO593 

0-00150 

0*0006 

o'oSn 

0-0232 

0-00597 

0-001503 

0-0006 

cf.  Fay  and  Seeker,  /.  Amer.  Chem.  Soc.,35,  (1903),  641,  and 
Fay,  Seeker  and  Ferguson,  Polytechnic  Engineer,  10,  (1910), 
72,  who  give  among  others  the  following  reduction  temper- 
atures : — 


Carbon  monoxide. 

Hydrogen. 

Cupric  oxide 
Mercuric  oxide  (yellow)  .. 

75°  C. 
o°C. 

125°  C. 
5o°  C. 

Silver  oxide  is  reduced  by  carbon  monoxide  at  the  ordinary 
temperature. 

On  similar  lines  is  the  observation  of  Henry  (Phil.  Trans., 
(1824),  266  ;  Phil.  Mag.,  [3],  9,  (1836),  324),  that  when  a 
mixture  of  carbon  monoxide,  hydrogen  and  oxygen  is 
exposed  to  a  platinum  catalyst  at  a  temperature  of  150- 
170°  C.,  the  oxygen  attaches  itself  mostly  to  the  carbon 
monoxide  ;  similar  results  were  obtained  at  the  ordinary 
temperature  (cf.  also  p.  255). 

It  is  evident  that  carbon  monoxide  is  an  energetic 
reducing  agent  and  many  of  its  applications,  usually  as 
producer  gas  or  water  gas,  depend  on  this  property.  It 


240  INDUSTRIAL   GASES 

slowly   reduces   silver   nitrate  solution,  potassium  perman- 
ganate solution,  etc.,  at  the  ordinary  temperature. 

Carbon  monoxide  reacts  readily  with  hydrogen  in  the 
presence  of  finely  divided  nickel  (Sabatier  and  Senderens, 
Comptes  Rend.,  134,  (1902),  514),  best  at  a  temperature  of 
250-300°  C.  according  to  the  equation- 

CD  +  3H2  ==  CH4  +  H20  +  5o,8oo  calories. 
It  is  patent  that  methane  production  will  be  favoured  by 
low  temperature—  consistent  with  sufficient  reaction  velocity 
—  and  high  pressure.  The  reaction,  however,  goes  very  com- 
pletely at  the  ordinary  pressure  if  excess  hydrogen  be  used 
at  250-300°  C.,  and  a  rough  calculation  according  to  the 
Nernst  Heat  Theorem  shows  that  starting  with  a  mixture 
containing  80  %  hydrogen—  which  with  complete  reaction 
would  give,  after  removing  water,  a  product  containing  50  % 
methane  and  50  %  hydrogen—  the  equilibrium  constant  at 
300°  C.  is  equal  to 


Pco  Xp*n2 

,.,      (     50,800  ) 

=  antilog<  —  —    --  3-5  log  573  —  2'2  > 
K57IX573      J^  } 

=  3'5  Xio? 

It  is  evident  that  very  little  carbon  monoxide  can  remain 
in  equilibrium  and,  approximating,  by  taking  pH^  =  pcli^ 
=  Pnzo  =  0*333  atm.,  we  have 

pco  =     Q-333XO-333 

3-5  X  10*  X  0-3333 
=  8'6  X  io~8  atms. 
=  o-  0000086  %  carbon  monoxide. 

At  a  temperature  of  800°  C.  a  similar  rough  calculation 
gives  a  value  of  0*0035  for  the  equilibrium  constant.  (The 
question  is,  of  course,  complicated  to  some  extent  by  the  water 
gas  reaction  owing  to  which  some  of  the  carbon  monoxide  will 
be  converted  to  carbon  dioxide.)  This  corresponds  to  a  final 
methane  content  of  only  about  1*7  %  when  starting  with  the 
above-mentioned  mixture.  In  this  connection  cf.  the 


CARBON  MONOXIDE  241 

production  of  hydrogen  by   the   decomposition  of  hydro- 
carbons, p.  189. 

As  an  impurity  of  technical  hydrogen  carbon  monoxide 
is  important  in  the  synthetic  production  of  ammonia 
and,  in  a  lesser  degree,  in  the  catalytic  hydrogenation 
of  oils.  For  the  latter  case  cf.  Maxted  (Trans.  Faraday 
Soc.,  Dec.,  1917),  according  to  whom  the  presence  of 
0*25  %  carbon  monoxide  in  the  hydrogen  effects  a  reduction 
in  the  rate  of  absorption  of  about  30  %.  The  sensitivity 
to  carbon  monoxide,  however,  depends  on  the  conditions  of 
preparation  of  the  nickel  catalyst;  thus,  lyessing  (B.P. 
18998/12)  introduces  the  nickel  catalyst  in  the  form  of  nickel 
carbonyl. 

The  illuminating  effect  of  carbon  monoxide  as  regards 
incandescent  mantles  is  found  by  Forshaw  to  be  48  % 
greater  than  that  of  hydrogen,  although  the  calorific  value 
is  only  18  %  greater. 

Carbon  monoxide  forms,  with  various  metals,  an  interest- 
ing series  of  additive  compounds,  a  description  of  some  of 
which  will  be  given  later. 

On  cooling,  carbon  monoxide  condenses  to  a  colourless 
liquid  and  solidifies  to  a  snowy  solid. 

The  limits  of  inflammability  of  carbon  monoxide  in 
admixture  with  air  are  as  follows  : — 

Minimum  percentage  of  air  in  carbon)  __       « 
monoxide  for  inflammation      . .     j  ~ 

Minimum      percentage      of     carbon  1  _ 
monoxide  in  air  for  inflammation  )  " 

(Coward,  see  p.  40). 

Manufacture  of  Carbon  Monoxide.— Carbon  monoxide 
is  seldom  made  in  a  pure  state  on  the  large  scale,  but  if 
required  it  is  readily  obtained  by  passing  carbon  dioxide 
through  a  bed  of  incandescent  coke.  The  operation 
may  be  rendered  continuous,  if  desired,  by  the  addi- 
tion of  oxygen  to  the  carbon  dioxide  (cf.  I^oiseau,  B.P. 
11590/08).  Reference  to  p.  238  will  show  that  a  tem- 
perature of  not  less  than  1000°  C.  is  desirable  if  comparative 
A.  16 


242  INDUSTRIAL   GASES 

freedom  from  carbon  dioxide,  without  subsequent  puri- 
fication, is  necessary.  With  this  ideal  in  view  Benjamin 
(U.S.P.s  1225048/17  and  1225396/17)  proposes  the  use 
of  local  electric  heating  of  the  carbon  dioxide  or  coal. 
According  to  B.P.  21213/13  of  the  "  Athion  "  Gesellschaft, 
the  necessary  carbon  dioxide  is  obtained  by  concentration 
from  products  of  combustion,  using  alkali  carbonate  lye 
(cf.p.  264). 

Carbon  monoxide  is  also  obtained  in  a  relatively  pure 
state  as  a  by-product  of  the  lyinde-Frank-Caro  process, 
the  liquid  fraction  usually  consisting  of  80-85  %  carbon 
monoxide  (cf.  p.  172)  the  remainder  being  hydrogen.  In 
most  cases  the  carbon  monoxide  is  burnt  in  a  gas  engine  for 
the  production  of  the  necessary  power  for  driving  the  com- 
pressors, etc.,  but  could  quite  well  be  used  for  chemical 
purposes,  e.g.  in  the  Mond  nickel  process  (cf.  p.  243). 

By  far  the  most  important  industrial  form  of  carbon 
monoxide,  however,  is  as  producer  gas  and  water  gas  (cf. 
Section  XIII.),  the  latter  of  which  contains  some  40%  carbon 
monoxide.  Coal  gas  also  contains  a  large  amount  of  carbon 
monoxide. 

Carbon  monoxide  may  be  prepared  in  a  pure  state  on  a 
semi-technical  scale  by  the  action  of  sulphuric  acid  on 
commercial  formic  acid.  Suitable  apparatus  for  this  purpose 
is  described  by  Hutton  and  Petavel  (loc.  cit.,  p.  113)  consist- 
ing of  a  large  glass  bolthead  half  filled  with  2  gallons  of 
sulphuric  acid  of  S.G.  173  and  heated  to  150-170°  C.  by 
means  of  a  granular  carbon  electric  resistance  furnace. 
Ninety  per  cent,  formic  acid  is  run  in,  when  carbon  monoxide 
(of  99  %  purity  after  washing  with  caustic  soda  solution)  can 
be  produced  at  a  rate  of  about  TOO  ft.3/hr.  and  at  a  cost 
of  some  50 /-  per  1000  ft.3.  About  130  Ibs.  of  the  90  % 
formic  acid  are  required  for  1000  ft.3  of  the  gas. 

Applications  of  Carbon  Monoxide 
General. — It  is  a  little  difficult  to  draw  any  sharp  line 
of  distinction  between  the  uses  of  carbon  monoxide  as  such 
and  the  general  applications  of  water  gas  and  semi-water 


CARBON  MONOXIDE  243 

gas,  but  among  the  former  may  be  emphasized  the  following 
examples  : — 

The  Mond  Nickel  Process. — Metallic  Carbonyls. — Be- 
fore describing  in  detail  this  interesting  process,  it  will  be 
well  to  give  a  brief  outline  of  the  production  and  character- 
istics of  the  additive  compounds  of  carbon  monoxide  with 
metals.  The  first  known  compound,  namely,  nickel  carbonyl, 
was  discovered  by  Mond  and  ganger  about  1889  somewhat 
as  follows.  At  this  time  a  process  was  in  use  by  Mond  for 
the  production  of  chlorine  from  ammonium  chloride  in 
which  nickel  oxide  was  heated  in  the  vapour  of  the  ammo- 
nium chloride,  giving  free  ammonia  and  nickel  chloride 
which  was  subsequently  reconverted  into  oxide  and  chlorine 
by  heating  in  air.  The  nickel  was  used  in  the  form  of  balls 
made  up  with  china  clay  and  was  found  to  deteriorate  rapidly, 
the  effect  being  traced  to  the  use  of  "  inert "  gas  for  the 
purpose  of  sweeping  out  the  residual  ammonia  before  admis- 
sion of  air.  The  "  inert  "  gas  consisted  of  nitrogen  containing 
some  carbon  monoxide  and  carbon  dioxide,  obtained  from 
the  ammonia  soda  plant.  In  like  manner,  attack  on  the 
nickel  valves  was  noticed.  These  observations  led  to 
the  study  of  the  action  of  carbon  monoxide  on  nickel  with 
the  object  of  making  any  possible  compounds.  During  the  in- 
vestigation the  exit  gases  from  the  experimental  tube  were  led 
to  a  Bunsen  burner  to  burn  up  the  poisonous  carbon  monoxide, 
and  to  the  surprise  of  the  investigators,  in  one  experiment 
when  the  tube  was  cooling  down,  particularly  when  below 
100°  C.,  the  flame  was  observed  to  become  luminous,  owing,  as 
was  subsequently  shown,  to  the  formation  of  nickel  carbonyl. 

Nickel  carbonyl — Ni(CO)4 — is  a  colourless  liquid  of  B.Pt. 
43°  C.  and  M.Pt— 25°  C.  The  vapour  is  liable  to  explode, 
even  at  60°  C.,  while  the  liquid  slowly  decomposes  in  the 
air,  giving  a  greenish  deposit.  On  heating  to  about  180°  C. 
metallic  nickel  is  deposited  in  the  form  of  a  mirror.  The 
compound  is  very  poisonous. 

The  equation 

Ni-f 


244  INDUSTRIAL   GASES 

indicates  that  the  formation  will  take  place  more  readily 
at  increased  pressures.  According  to  Dewar  the  dissociation 
pressure  of  nickel  carbonyl  varies  with  the  temperature  as 
follows  : — 

Temperature.  Dissociation  pressure 

(experimental). 

100°  C.         . .         . .         . .         15  atms. 

250°  C          100  atms. 

Iron  likewise  forms  compounds  under  similar  conditions. 
The  compound  most  easily  formed  is  the  pentacarbonyl — 
Fe(CO)6— a  yellow  liquid  of  B.Pt.  IO2'8°  C.  By  the  action 
of  light  it  is  converted  into  Fe2(CO)9,  an  orange  red  crystalline 
substance  which  in  turn,  when  dissolved  in  toluene  and  heated 
to  95°  C.  in  an  atmosphere  of  carbon  dioxide,  gives  Fe(CO)4. 

Iron  carbonyl  is  formed  in  small  quantities  in  cylinders 
containing  compressed  water  gas  or  coal  gas  by  the  action 
of  the  carbon  monoxide  on  the  iron  of  the  cylinders  and  has  a 
deleterious  action  when  such  coal  gas  is  used  for  limelight 
or  for  incandescent  mantles,  the  iron  being  deposited  in  the 
form  of  oxide.  The  formation  of  the  compound  may  be 
minimized  by  special  treatment  of  the  cylinders. 

It  was  long  thought  that  cobalt  gave  no  parallel  compound, 
but,  in  1910,  Mond,  Hirtz  and  Cowap  (Chem.  Soc.  Trans., 
(1910),  798)  isolated  the  carbonyls  of  cobalt,  molybdenum 
and  ruthenium.  These  compounds  have  higher  dissociation 
pressures  than  the  corresponding  nickel  and  iron  compounds. 
Thus  the  conditions  for  their  formation  are — 

Pressure.  Temperature. 

Atms.  °C. 

Cobalt 100  200 

Molybdenum    . .         . .     250  200 

Ruthenium       . .         . .     450  300 

Potassium  with  carbon  monoxide  at  80-90°  C.  forms 
a  black,  solid  explosive  compound  (KCO),  which  detonates 
at  100°  C.,  or  by  contact  with  air  or  water  at  the  ordinary 
temperature.  The  formation  of  this  compound  was  a 
source  of  considerable  trouble  in  the  old  process  of  manu- 
facturing potassium. 


CARBON  MONOXIDE  245 

The  Refining  of  Nickel  by  the  Mond  Process. — Following 
up  the  results  of  the  above-mentioned  investigation  Mond 
developed  the  process  on  a  technical  scale.  In  a  very 
comprehensive  patent,  B.P.  12626/90,  Mond  outlines  a  method 
of  refining  nickel  based  on  the  alternate  formation  and  decom- 
position of  nickel  carbonyl.  A  number  of  patents  follow, 
e.g.  B.P.  8803/91  relates  to  the  direct  production  of  nickel 
alloys  by  passing  the  gas  containing  nickel  carbonyl  into  a 
molten  metal ;  B.P.s  23665/91  and  23665A/9I  describe 
the  arrangement  of  the  reducer  and  the  volatilizer  with  an 
intermediate  rotatory  feed  valve  for  the  ore  to  prevent 
intermixing  of  the  gases,  while  B.P.  1106/98  prescribes  the 
use  of  pellets  as  media  for  the  continuous  deposition  of  the 
nickel  with  appropriate  plant.  These  patents  form  the 
basis  of  the  process  as  described  below.  In  B.P.  9300/02 
Dewar  deals  with  the  action  of  increased  pressure  in  the 
operation  of  the  process,  but  this  modification  does  not  appear 
to  have  come  into  use  in  actual  working  ;  the  enhanced 
formation  of  the  carbonyl  would  doubtless  be  largely  offset 
by  the  increased  cost  and  difficulty  of  conducting  operations 
under  high  pressure. 

An  experimental  large-scale  plant  was  erected  at  Smeth- 
wick  in  1892  and  after  the  success  of  the  process  had  been 
demonstrated,  a  large  works  was  put  up  at  Clydach,  the 
present  output  of  which  amounts  to  some  3000  tons  of  nickel, 
of  99 '9  %  purity,  per  annum.  Details  of  the  present  plant 
are  not  available,  but  presumably  it  is  similar  to  the  Smeth- 
wick  plant,  of  which  a  description  is  given  by  Mond  in  Revue 
Gen.  de  Chim.  pure  et  app.,  2,  (1900),  121.  The  scheme  of 
the  operations  is  as  follows.  Nickel  ores  containing  nickel, 
cobalt,  copper  and  iron  as  pyrrhotite  (magnetic  pyrites), 
kupfernickel,  chalcopyrite,  etc.,  are  suitable.  That  usually 
adopted  is  pyrrhotite  mixed  with  copper  pyrites  and  is 
essentially  iron  sulphide  containing  some  3  %  nickel  and 
about  the  same  quantity  of  copper  ;  the  principal  deposits 
are  in  Sudbury.  The  bessemerized  matte,  containing  some 
80  %  Ni  -f-  Cu,  is  roasted  to  convert  it  into  oxide  when  it 
contains  about  Ni  35  %,  Cu  42  %,  Fe  5  %.  It  is  next  crushed 


246  INDUSTRIAL  GASES 

and  screened  through  a  6o-mesh  sieve  and  then  enriched 
in  nickel  by  leaching  with  dilute  sulphuric  acid  which 
dissolves  out  part  of  the  copper,  the  ore  having  a  final 
composition  of  about  Ni  51  %,  Cu  21  %,  Fe  3  %.  After 
drying,  the  ore  passes  to  the  "  reducing  "  and  "  volatilizing  " 
towers,  which  are  superimposed,  the  latter  being  on  top. 
By  means  of  annular  flues  heated  by  producer  gas,  the 
"  reducer,"  which  is  some  25  ft.  high,  is  maintained  at  a 
temperature  not  exceeding  300°  C.  The  "  reducer  "  and  also 
the  "  volatilizer  "  are  provided  with  shelves  and  mechanically- 
operated  rabbles  revolving  round  a  central  vertical  shaft, 
as  in  a  Herreshoff  sulphur  burner,  the  ore  being  fed  in  at  the 
top,  passing  from  centre  to  periphery  and  vice  versa;  the 
reducer  has  about  14  shelves. 

The  nickel  and  copper  oxides  are  thus  reduced  by  a  stream 
of  water  gas  passing  upwards  as  the  ore  descends  the  tower, 
the  reduced  product  is  cooled  to  about  50°  C.  on  the  lower 
5  shelves,  this  section  of  the  tower  being  water-jacketed. 
From  the  bottom  of  the  "  reducer  "  the  reduced  ore  is  passed 
out  through  a  rotating  valve  and  is  lifted  by  means  of  an  air- 
tight conveyor  to  the  top  of  the  "  volatilizer."  This  tower, 
which  is  about  15  ft.  in  height,  is  maintained  at  about  50- 
100°  C.  Here  the  reduced  ore  passes  down  in  counter- 
current  to  a  stream  of  80  %  carbon  monoxide  which  effects 
the  formation  of  nickel  carbonyl,  the  carbon  monoxide 
effluent  having  a  carbonyl  content  of  about  2  %.  The  ore, 
on  the  other  hand,  passes  out  through  a  rotating  valve,  which 
prevents  the  intermixing  of  the  two  types  of  gas,  and  back 
to  the  reducer. 

This  cyclic  treatment  is  necessary,  as  the  nickel  after  a 
time  loses  its  power  of  yielding  carbonyl  and  requires  reacti- 
vation by  further  heating  to  300°  C.  in  the  reducing  gases. 

The  gases  leaving  the  volatilizer  pass  through  a  dust  filter 
and  enter  the  decomposer,  which  consists  of  a  tower  some 
10  ft.  high  filled  with  nodules  of  nickel  previously  formed, 
and  heated  to  180°  C.  Entering  at  the  top,  the  gases  pass 
down  through  a  central  pipe  reaching  to  the  bottom  and 
perforated  along  its  length,  the  nickel  carbonyl  suffering 


CARBON  MONOXIDE 


247 


decomposition  among  the  pellets  of  nickel  which  gradually 
increase  in  size  ;  the  pellets  pass  out  at  the  bottom  of  the 
tower  through  a  rotating  valve  and  are  automatically 
screened,  the  smaller  ones  being  returned  to  the  top  of  the 
tower  by  an  elevator  while  the  larger  pass  out  through  a 
valved  opening.  In  consequence  of  the  constant  friction, 
the  nodules,  as  put  on  the  market,  have  the  appearance  of 
burnished  bicycle  balls  of  about  J  in.  diameter.  This  system 
of  operating  the  decomposer  avoids  any  trouble  in  the  other- 
wise intermittent  removal  of  the  deposited  nickel.  The 
disengaged  carbon  monoxide  returns  to  the  volatilizer. 
To  prevent  blocking  by  deposition  of  nickel  carbonyl  within 
the  central  pipe,  the  latter  is  water-jacketed.  We  have 
here  a  very  ingenious  series  of  cyclic  operations  represented 
graphically  in  Fig.  22. 


H8S04 


RESIDUE     FROM     EXTRACTION 
=  Mi    40%    Co  35%   Fa  5%   (o>t'!«r 

FIG.  22. — Mond  Nickel  Process. 

It  is  important  that  the  temperature  of  the  reducer 
should  not  exceed  300°  C.,  especially  if  much  iron  be  present, 
as  the  reduction  of  the  iron  oxide  would  give  rise  to  iron 
pentacarbonyl  with  consequent  contamination  of  the  metallic 
nickel.  Further,  an  increase  of  temperature  impairs  the 
activity  of  the  reduced  nickel  as  regards  carbonyl  formation. 
Reduction  is  carried  out  by  water  gas  containing  about 
60  %  hydrogen,  from  anthracite  generators ;  under  the 
above  conditions  the  reduction  is  mostly  affected  by  the 
hydrogen,  of  which  the  issuing  gas  contains  only  about 
5-10  %.  Part  of  this  gas,  after  passing  first  through  a 
cooler  and  then  through  a  retort  filled  with  incandescent 


248  INDUSTRIAL   GASES 

wood  charcoal  and  now  containing  some  80  %  carbon 
monoxide,  is  used  to  make  up  the  losses  from  the  volatilizer- 
decomposer  cycle.  The  ore  is  circulated  through  the  volati- 
lizer  until  about  60  %  of  the  nickel  is  removed  (residue  equals 
about  two-thirds  of  the  original  matte),  this  conversion 
occupy  ing  from  8  to  15  days,  and  is  then  of  similar  composition 
to  the  original  matte.  It  is  returned  to  the  roasting  furnace, 
leached  and  put  into  commission  again.  Some  care  is 
required  as  regards  the  temperature  of  the  decomposer. 
If  less  than  180°  C.  the  nickel  is  not  deposited,  and  if  above 
180-200°  C.  catalytic  dissociation  of  the  carbon  monoxide 
to  carbon  dioxide  and  carbon  is  induced. 

As  stated  above,  the  purity  of  the  nickel  is  extremely 
high,  the  carbon  content,  which  is  often  of  importance,  being 
less  than  0*1  %. 

The  Production  of  Formates,  Oxalates  and  Acetates. 
— The  action  of  carbon  monoxide  on  heated  caustic  soda  was 
discovered  by  Berthelot  in  1856,  who  showed  the  action  to 
proceed  according  to  the  equation — 

CO  +  NaOH  =  H  .  COONa 

and  observed  that  the  absorption  proceeded  more  rapidly 
in  the  presence  of  water. 

A  more  complete  investigation  of  the  reaction  from  a 
technical  standpoint  was  undertaken  by  Weber  ("  Uber  die 
Einwirkung  von  Kohlenoxyd  auf  Natronlauge,"  Karlsruhe 
Dissertation,  1908).  Working  with  increased  pressure  and 
at  temperatures  up  to  180°  C.,  Weber  arrived  at  the  following 
conclusions :  (i)  that  the  reaction  is  of  the  first  order  ;  (2) 
that  a  solution  containing  10  %  NaOH  gives  the  highest 
reaction  velocity  at  high  temperatures  ;  (3)  that  the  reaction 
occurs  between  the  dissolved  carbon  monoxide  and  the 
caustic  soda,  not  between  gaseous  carbon  monoxide  and 
water  vapour;  and  (4)  that  for  constant  temperature  and  speed 
of  stirring  the  rate  of  absorption  is  proportional  to  the 
concentration  of  carbon  monoxide. 

The  experiments  were  continued  by  Fonda  ("  Uber  die 
Einwirkung  von  Kohlenoxyd  auf  I^augen,"  Karlsruhe 


CARBON  MONOXIDE  249 

Dissertation,  1910)  and  are  summarized  by  Haber  in  his 
Hurter  memorial  lecture  at  lyiverpool  (/.  Soc.  Chem.  Ind., 
(1914),  51).  At  a  comparatively  low  temperature,  stirring 
had  little  influence,  the  liquid  being  easily  kept  saturated 
with  gas,  but  when  a  temperature  of  160-170°  C.  was 
reached,  the  stirring  could  not  be  made  so  fast  that  an 
increase  in  the  speed  did  not  cause  an  increased  rate  of 
reaction.  Above  100°  C.,  10  %  NaOH  gave  the  best  results, 
e.g.  Sit  160°  C.  the  reaction  velocity  was  more  than  15  times  as 
great  with  10  %  as  with  43  %  solution.  It  was  thought 
possible  that  the  superiority  of  the  10  %  solution  might  be 
explained  by  a  connection  with  the  surface  tension,  but  this 
hypothesis  was  not  confirmed  by  measurements  of  the  latter 
at  the  high  temperatures  in  question. 

Experiments  by  Bredig  and  Carter  at  temperatures  of 
50-80°  C.  and  pressures  up  to  40  atms.,  using  different 
bases,  e.g.  the  alkalis,  baryta,  tetramethylammonium  hydrox- 
ide, piperidene,  etc.,  showed  that  the  reaction  velocity  was 
constant  for  different  bases  given  equal  hydroxydion 
concentration. 

There  are  many  patents  relating  to  this  subject,  among 
which  the  following  may  be  mentioned :  B.P.  17066/95, 
by  Goldschmidt,  relates  to  the  production  of  formate  by 
passing  carbon  monoxide  over  caustic  soda,  or  preferably 
soda-lime,  at  a  temperature  of  about  230°  C.,  the  operation 
being  facilitated  by  being  carried  out  under  pressure. 
According  to  Koepp  &  Co.  (B.P.  7875/04)  a  35  %  solution 
of  caustic  soda  is  run  on  to  a  mass  of  coke  at  a  temperature  of 
220°  C.  in  a  closed  vessel ;  carbon  monoxide  is  passed  through 
the  liquid  for  three-quarters  of  an  hour.  In  B.P.  772/06,  the 
Elektrochemische  Werke,  Bitterfeld,  prescribe  the  treatment 
of  caustic  alkali  in  large  pieces  with  carbon  monoxide  at  100- 
120°  C.  under  pressure,  while  Nitridfabrik,  G.m.b.H.  (B.P. 
9008/06)  deals  with  the  use  of  caustic  soda  with  the  addition 
of  0-12  %  to  0-15  %  water,  such  addition  of  water  being 
claimed  to  produce  improved  absorption.  In  B.P.  i3953/°7 
the  United  Alkali  Co.  and  others  claim  an  accelerated  and 
more  complete  absorption  when  using  solid  caustic  soda,  by 


250  INDUSTRIAL  GASES 

the  addition  of  titanium  compounds,  e.g.  a  mixture  of  caustic 
soda  with  about  n  %  titanic  acid  is  used  at  a  temperature 
of  about  150°  C.  After  evacuation,  carbon  monoxide  is 
admitted  with  stirring,  the  pressure  being  kept  low.  Ellis 
and  McKlroy  (U.S. P.  875055/07)  prescribe  the  treatment 
of  basic  mineral  substances,  e.g.  calcium  carbonate,  suspended 
in  water,  with  carbon  monoxide  or  producer  gas  at  high 
temperature  and  pressure.  Dubox,  L,uttinger  and  Denis 
(F.P.  421227/09)  advocate  the  use  of  ammonia  or  organic 
bases  in  presence  of  pumice  impregnated  with  one  of  a  number 
of  metallic  catalysts  at  a  temperature  of  90-165°  C.  and  at 
atmospheric  pressure.  On  somewhat  similar  lines  is  U.S. P. 
1212359/17,  by  Katz  and  Ovitz,  according  to  whom  a  stream 
of  carbon  monoxide  and  ammonia  ascending  a  tower,  meets  a 
descending  stream  of  finely  divided  caustic  alkali  solution,  the 
temperature  being  150-200°  C.  and  the  pressure  10-20  atms. 

The  synthetic  production  of  formates  is  carried  out 
on  a  considerable  scale,  the  usual  source  of  carbon  monoxide 
being  air  producer  gas. 

In  the  manufacture  of  formates,  especially  when  carried 
out  under  increased  pressure,  the  action  of  caustic  soda 
liquor  on  steel  at  high  temperatures  is  of  importance  from  a 
safety  standpoint.  Hydrogen  is  absorbed  by  the  steel, 
the  mechanical  properties  of  which  are  impaired.  Cf. 
Andrew,  Trans.  Faraday  Soc.,  9,  (1914),  317  ;  Mercia,  Metall. 
and  Chem.  Eng.,  16,  (1917),  496,  503  ;  Stromeyer,  Chem. 
Trade].,  61,  (1917),  533  ;  Worsley,  Ibid.,  62,  (1918),  65. 

ProductionofOxalates. — On  gentle  heating,  sodium  formate 
is  easily  converted  into  oxalate  with  liberation  of  hydrogen 
and  the  following  patents  relate  to  such  conversion. 

Goldschmidt  (B.P.  26172/97)  heats  sodium  formate 
mixed  with  about  125  %  of  anhydrous  sodium  carbonate 
to  400-410°  C.,  the  sodium  carbonate  securing  a  good  yield 
of  oxalate  and  being  subsequently  removed.  Similarly, 
Koepp  &  Co.,  in  B.P.  9327/03,  heat  sodium  formate  with 
e.g.  i  %  of  caustic  soda  which  facilitates  the  decomposition. 
At  260°  C.  the  molten  mixture  evolves  hydrogen  and  the 
reaction  is  complete  at  ^60°  C.  The  use  of  reduced  pressure 


CARBON  MONOXIDE  251 

is  prescribed  in  B.P.  19943/07  by  the  Elektrochemische 
Werke,  Bitterfeld,  the  conversion  taking  place  at  a  lower 
temperature,  preferably  about  280°  C. 

Other  patents  have  as  their  primary  object  the  production 
of  mixtures  of  nitrogen  and  hydrogen  through  the  intermedi- 
ary of  formates,  e.g.  B.P.  30073/13  and  U.S.P.  1098139/14 
(cf.  p.  205),  while  B.P.  1759/12  relates  to  the  removal 
of  the  last  traces  of  carbon  monoxide  from  hydrogen 
(cf.  p.  208). 

Acetates  may  be  produced  in  a  similar  manner  to  formates 
by  the  treatment  of  sodium  methoxide  with  carbon  monoxide 
at  a  temperature  of  180°  C. 

The  Production  of  Gases  Rich  in  Methane.— Carbon 
monoxide  reacts  readily  with  hydrogen  to  form  methane  in 
the  presence  of  a  suitable  catalyst,  as  stated  on  p.  240.  The 
method  has  been  used  on  the  large  scale  for  the  production 
from  water  gas  of  a  gas  of  high  calorific  power  with  some 
illuminating  properties. 

A  description  is  given  by  Krdmann  (/.  Gasbeleucht.,  54, 
(1911),  737)  of  an  experimental  plant  installed  in  England 
by  the  Cedford  Gas  Producing  Co.  (cf.  B.P.s  17017/09  and 
22219/09).  In  order  to  obtain  a  gas  of  suitable  composition 
(as  the  action  is  unsatisfactory  in  the  presence  of  excess 
carbon  monoxide),  the  water  gas  was  given  a  preliminary 
treatment  in  a  lyinde-Frank-Caro  plant  (cf.  p.  172),  the 
valves  being  so  regulated  as  to  give  a  gaseous  fraction 
containing  about  17  %  carbon  monoxide,  e.g.  in  one 
test  the  average  percentage  composition  of  the  gas  was — 

Hydrogen     .  .          . .          . .          . .      80*9 

Carbon  monoxide  .  .          . .          . .       16*3 

Nitrogen      . .         . .          .  .          .  .        2'8 

lOO'O 

Part  of  the  liquid  (carbon  monoxide)  fraction  was  used 
for  the  driving  of  the  compressors.  This  preliminary 
treatment  had  the  advantage  of  giving  a  gas  completely 
free  from  sulphur  compounds  which  exert  a  poisonous  effect 


252  INDUSTRIAL  GASES 

on  the  nickel  catalyst.  The  above  gas  mixture  was  passed 
through  three  vertical  quartz  tubes  of  4!  in.  internal  diameter 
and  about  5  ft.  long  containing  pumice  impregnated  with 
about  200  grams  of  nickel  per  tube.  The  tubes  were  electri- 
cally heated  to  280-300°  C.,  the  gas  being  also  preheated ;  after 
working  for  a  little  time  the  operation  was  self-supporting, 
leaving  through  a  condenser  the  gases  had  the  following 
percentage  composition : — 

Hydrogen  .62 

Methane  . .          . .          . .  31 

Nitrogen  . .          . .          . .          . .       6 

Carbon    monoxide,    carbon    dioxide, 
etc Traces. 

and  possessed  a  calorific  value  of  263  C.H.U./ft.3,  (474 
B.T.U.)  as  against  the  initial  value  of  159  C.H.U./ft.3 
(286  B.T.U.)  for  the  original  water  gas. 

About  450  ft.3/hr.  of  the  16  %  carbon  monoxide  gas  was 
passed  through  the  catalytic  chambers,  which  had  a  volume  of 
about  i "8  ft.3,  corresponding  to  a  "  space  velocity  "  of  250 
ft.3/ft.3  catalyst  space/hour,  referred  to  the  16  %  carbon 
monoxide  gas,  or  of  128  referred  to  the  final  gas.  The  cost 
of  conversion  of  the  water  gas  into  the  final  product  is  given 
as  176^71000  ft.3  of  the  latter  ;  this  figure  would  appear 
to  be  low  and  in  any  case  does  not  include  any  overhead 
charges. 

The  Manufacture  of  Phosgene — Carbonyl  chloride, 
or  phosgene,  is  an  industrial  gas  which  may  be  conveniently 
described  at  this  point  on  account  of  its  manufacture  from 
carbon  monoxide.  By  passing  a  mixture  of  carbon  monoxide 
and  chlorine  over  platinum  sponge  at  400°  C.,  combination 
takes  place  yielding  phosgene,  according  to  the  following 
reversible  reaction : — 

CO  +  C12^COC12  +22,950  calories. 

The  equilibrium  is  given  below  for  a  pressure  of  one 
atmosphere,  the  values  being  calculated  according  to  the 


CARBON  MONOXIDE 


253 


Nernst    Heat    Theorem    (cf.    Horak,    Dissertation,    Berlin, 
1909). 

TABLE  27. 
PHOSGENE  EQUILIBRIUM. 


Temperature  °C. 

%  COC12 

%  CO 

%  CI2 

300 
400 
500 

92-5 

66-9 

29*0 

3-75 

I6'5 
35'  5 

3'  75 
16-5 
35'  5 

It  is  evident  that  a  low  temperature  is  favourable  to  the 
production  of  the  carbonyl  chloride  and  that  increase  of 
pressure  would  also  favour  the  reaction.  The  reaction 
takes  place  in  the  presence  of  animal  charcoal  as  catalyst, 
either  in  the  dark  or,  better,  in  sunlight.  Thus,  according  to 
a  small-scale  experiment  of  Paterno,  70  c.c.  of  animal  charcoal 
effect  the  formation  of  about  i  kilo,  carbonyl  chloride  in  24 
hours,  corresponding  to  a  "  space-time-yield  "  of  about  o-6 
kilos.  /litre  catalyst/hour.  On  the  large  scale,  with  coarse 
granulated  charcoal  in  the  dark,  a  considerably  lower  space- 
time-yield  is  to  be  expected.  Cooling  is  necessary  on  account 
of  the  heat  evolution. 

Phosgene  has  also  been  manufactured  by  heating  together 
electrically  a  mixture  of  quicklime,  calcium  chloride  and 
ground  coke  — 


2CaO  +  2CaCl2  -f  icC  =  4CaC2  +  2COC12 

Calcium  carbide  is  formed  while  phosgene  distils  over  and  may 
be  at  once  converted  into  carbon  tetrachloride  by  passing 
through  a  heated  catalyst,  e.g.  coke,  bone  black,  pumice, 
etc.,  carbon  dioxide  being  formed  at  the  same  time  with 
evolution  of  heat.  (Cf.  U.S.P.  808100/05  by  Machalske.) 

Properties  and  Uses  of  Phosgene.  —  Phosgene  is  a  colourless 
gas  liquefying  at  8*2°  C.  It  has  a  characteristic,  unpleasant 
and  pungent  odour.  The  liquid  has  a  specific  gravity  of 
1-432  ato°  C.  The  substance  is  decomposed  slowly  by  cold, 
rapidly  by  hot  water.  It  is  fairly  reactive  and  is  used  on 


254  INDUSTRIAL   GASES 

a  considerable  scale  for  the  preparation  of  di-  and  tri-phenyl- 
methane  dyestuffs,  etc.  It  combines  with  ammonia  to  form 
urea  and  ammonium  chloride.  Phosgene  is  sold  in  the 
liquid  state  in  cylinders. 

With  reference  to  its  use  as  a  poison  gas,  see  p.  292.  It  is 
much  more  insidious  in  its  physiological  action  than  chlorine, 
being  less  irritant  while  its  effects  are  only  evident  after  a 
considerable  number  of  hours  and  are  then  very  severe. 

Other  Applications  of  Carbon  Monoxide. — The  use 
of  carbon  monoxide  has  been  proposed  for  the  reduction  of 
organic  compounds ;  cf.  B.P.  6409/15  of  the  Badische  Co., 
according  to  whom  nitro  compounds  as  e.g.  nitrobenzene,  are 
vaporized  and  passed  with  a  carbon  monoxide-steam  mixture 
over  a  copper  catalyst  on  pumice  at  a  comparatively  low 
temperature  ;  the  carbon  monoxide  is  converted  wholly  or 
partially  into  carbon  dioxide. 

Estimation  of  Carbon  Monoxide Carbon  monoxide 

may  be  detected  by  its  blackening  action  on  paper  moistened 
with  palladious  chloride  solution,  or  by  examination  of  the 
blood  of  animals,  e.g.  mice,  after  air  containing  carbon 
monoxide  has  been  breathed  by  them.  Carboxyhaemoglobin 
has  a  definite  absorption  spectrum  and  the  test  is  sensitive 
to  about  O'Oi  %.  When  present  in  sufficient  quantity 
carbon  monoxide  may  be  estimated  fairly  satisfactory  by 
absorption  in  cuprous  chloride  solution  after  preliminary 
removal  of  the  oxygen.  The  useful  lower  limit  of  the  method 
is  about  0*25  %  of  carbon  monoxide. 

By  passing  the  dry  gas  over  iodine  pentoxide  heated  to 
about  160°  C.,  any  carbon  monoxide  is  quantitatively 
oxidized  to  carbon  dioxide  according  to  the  equation — 

I2O6  +  2CO  =  I2  +  5CO2 

(cf.  Levy,  J.  Soc.  Chem.  Ind.,  (1911),  1437  ;  Graham,  Ibid., 
(1919),  10  T.)  By  means  of  this  reaction,  concentrations  of 
from  0-003  t°  0^0003  %  may  be  estimated  in  air  by  collecting 
the  iodine  formed.  In  the  presence  of  hydrogen,  in  which 
gas  the  necessity  of  estimating  small  quantities  of  carbon 
monoxide  often  arises,  the  results  are  complicated  by  a  small 


CARBON  MONOXIDE  255 

portion  of  the  hydrogen  undergoing  oxidation  ;  'it  is  conse- 
quently necessary  to  remove  the  iodine  first  by  cooling  and 
then  by  bubbling  through  mercury  which  effectively  removes 
iodine  vapour,  and  to  estimate  not  the  iodine  but  the  carbon 
dioxide  formed,  by  suitable  means.  Methane  is  not  attacked 
by  the  iodine  pentoxide,  but  any  unsaturated  hydrocarbons 
present  must  be  removed,  best  by  the  action  of  concentrated 
sulphuric  acid  at  a  temperature  of  about  165°  C.  (Weiskopf, 
/.  Soc.  Chem.Ind.,  (1909),  1170).  The  method  is  accurate, 
without  any  special  precautions,  to  about  O'oi  %,  provided 
that  effective  means  be  adopted  for  the  accurate  estimation 
of  the  carbon  dioxide. 

A  similar  preferential  oxidation  of  the  carbon  monoxide 
may  be  effected  by  the  action  of  chlorate  solutions  activated 
with  colloidal  osmium,  by  precipitated  mercuric  chromate 
(Hofmann,  Ber.,  49,  (1916),  1650,  1663)  ;  by  activated 
copper  oxide  moistened  with  alkali,  or  by  activated  copper 
moistened  with  alkali  in  the  presence  of  oxygen  (Hofmann, 
Ibid.,  51,  (1918),  1334)  »  a^so  by  the  action  of  precipitated 
mercuric  oxide  (Moser  and  Schmid,  J.  Soc.  Chem.Ind.,  (1914), 
442) .  An  automatic  carbon  monoxide  recorder,  designed  for 
estimation  of  this  gas  in  hydrogen,  has  been  described  by 
Rideal  and  Taylor  (Analyst,  March  1919).  It  depends  on 
the  catalytic  fractional  combustion  of  the  carbon  monoxide 
and  subsequent  estimation  of  the  carbon  dioxide  by  a  con- 
ductivity method. 


SECTION  IX.— CARBON  DIOXIDE 


Occurrence. — Carbon  dioxide  occurs  in  large  quantities 
in  a  pure  state,  issuing  from  fissures  in  the  earth,  usually 
in  the  neighbourhood  of  volcanoes ;  in  caverns,  especially 
in  limestone  districts,  and  also  with  water  in  mineral  springs, 
e.g.  the  mineral  springs  of  the  Volcanic  Eifel  and  other 
springs  in  Germany  and  France,  the  Saratoga  springs  in 
New  York,  etc.  In  addition,  carbon  dioxide  is  present  in 
small  quantities  in  the  air  (cf.  p.  59), 

Properties  of  Carbon  Dioxide.  — Carbon  dioxide 
(carbonic  anhydride,  carbonic  acid  gas)  is  a  colourless  gas 
with  a  slight  acid  odour  and  taste.  It  is  characterized  by 
being  easily  liquefiable  on  simple  application  of  pressure  at 
the  ordinary  temperature,  and  by  its  relatively  high  solu- 
bility in  water. 

The  following  table  gives  the  relation  between  temper- 
ature, pressure  and  solubility  :  — 


Temperature  °C  

o 

5 

10 

i^ 

20 

,0 

40 

5° 

60 

C.c.  gas  at  N.T.P.  dissolved  by\ 

i  c.c.  of  water  under  a  pressure 

of  i  atm.  exclusive  of  water  V 

I-7I3 

1-424 

1-194 

1-019 

0-878 

0-665 

0-530 

0-436 

o'359 

vapour      (Bohr    and     Bock, 

Annalen,  44,  (1891),  318)       .  .  j 

At  increased  pressures  the  solubility  does  not  follow 
Henry 'slyaw  closely,  being,  according  to  Wroblewski  (Comptcs 
Rend.,  94,  (1882),  1355),  as  follows  :  — 


Pressure  in  atms.  (ab- 

solute) 

i 

5 

10 

15 

20 

25 

30 

Solubility  in  c.c.    per 

c.c.  water  at  i2'4°C. 

roS6 

5'i5 

9'65 

13-63 

I7-II 

20*31 

23^5 

CARBON  DIOXIDE 


257 


The  specific  heat  shows  a  much  larger  temperature 
coefficient  than  that  of  most  other  gases  being  given  by  the 
following  expression  (Holborn  and  Henning,  Annalen,  [4], 
18,  (1905),  7139;  23,  (1907),  809)  — 

C     =  0'20IO  -f  0-0000742£  —  0-OOOOOOOI&2 


over  the  range  0-1400°  C.  where  Cp  =  mean  specific  heat, 
and  t  =  °C.,  while  according  to  Crofts  (Chem.  Soc.  Trans., 
(1915),  290)— 

Cv  —  0-1500  +  0-000052^ 

where  C,,  is  the  mean  specific  heat  between  t  and  15*5°  C. 

Carbon  dioxide  passes  through  indiarubber  with  greater 
rapidity  than  do  most  other  gases  (cf.  p.  10). 

An  aqueous  solution  of  carbon  dioxide  is  slightly  acid 
to  litmus  ;  the  acid  H2CO3  is,  however,  almost  entirely 
undissociated.  Crystalline  hydrates  are  formed  at  low 
temperatures. 

On  heating  to  very  high  temperatures  carbon  dioxide 
undergoes  dissociation  into  carbon  monoxide  and  oxygen,  as 
is  seen  from  the  following  table  (*Nernst  and  v.  Wartenberg, 
Z.physik.  Chem.,  56,  (1906),  548  ;  f  Bjerrum,  Z.physik.  Chem., 
79,  (1912),  537)  :  — 

TABLE  28. 
DISSOCIATION  OF  CARBON  DIOXIDE. 


Temperature  °C. 

*I027 

*II27 

*I205 

t2367 

f26o6 

t262; 

f2672 

t2843 

Percentage    of    carbon 

dioxide     which     has 

undergone     dissocia- 

tion  .  . 

0-00414 

0-01-0-02 

0-029-0-035 

21'0 

51-7 

49-2 

64-7 

76-I 

These  values  are  determined  experimentally  for  a  pressure 
of  i  atmosphere. 

At  reduced  pressures  the  dissociation  is  more  pronounced. 

By  the  action  of  the  silent  discharge,  or  ultra-violet  light, 
dissociation  into  carbon  monoxide  and  oxygen  takes  place. 
For  a  discussion  of  the  equilibrium  between  carbon  dioxide, 
carbon  monoxide  and  carbon — 

CO2  -f  C  ^  2CO  —  39,300  calories, 
cf.  pp.  238  and  303. 

A.  17 


258  INDUSTRIAL  GASES 

The  conversion  of  carbon  dioxide  into  carbon  monoxide 
by  the  water  gas  reaction  has  also  been  dealt  with  elsewhere. 
Carbon  dioxide  is  converted  into  methane  by  passage  over 
reduced  nickel  at  350°  C.  in  like  manner  to  carbon  monoxide 
(Sabatier  and Senderens,  Comptes  Rend.,  134,  (1902),  514, 689). 

Carbon  dioxide  is  decomposed  by  heated  magnesium 
with  separation  of  carbon.  It  is  a  non-supporter  of 
combustion  and  on  this  account  is  employed  as  a  fire 
extinguisher.  Although  its  poisonous  action  is  slight,  it 
produces  suffocation  by  lowering  the  concentration  of  oxygen. 
Exhaled  air  contains  some  4-4  %  of  carbon  dioxide,  about 
2  Ibs.  being  expired  daily  by  an  average  adult.  Carbon 
dioxide  is  an  important  factor  in  the  rusting  of  iron  when 
oxygen  and  water  are  also  present.  At  high  temperatures 
carbon  dioxide  is  an  energetic  oxidizing  agent,  thus  metals 
such  as  iron  are  attacked  rapidly  by  the  gas  at  a  red  heat. 

It  has  been  observed  by  Fischer  (/.  Soc.  Chem.  Ind., 
(1915),  726)  that  carbon  dioxide  in  the  gaseous  state  behaves 
as  a  fertilizer  in  promoting  plant  growth. 

Liquid  Carbon  Dioxide. — liquid  carbon  dioxide  is  a 
colourless,  very  mobile  liquid,  having  the  following  vapour 
pressures  at  the  temperatures  specified  : — 


Temperature  °C. — 
Solid. 


—78*2   —70   —60   —50  —40  — 30    — 20    — 10      o       10      20      30       40 


Vapour  pressure  in  atms. 
(absolute) — 

35-4  46-0  58-8  73-8  91-0* 

34*3  44'2  56-3  70-7    —  t 
roo  1-88   3-92    6-73    9-88  14-21  19-52  25-83  J 


*  Regnault,  1862.          f  Amagat,  1892.         \  Zeleny  and  Smith,  1906. 

The  density  of  the  liquid  at  15°  C.  is  0*814  (Amagat). 
lyiquid  carbon  dioxide  is  only  slightly  soluble  in  water,  but 
is  readily  miscible  with  alcohol,  ether,  etc. 

For  further  information  as  to  properties,  see  Tables  12 
and  13,  also  pp.  42-45. 

Solid  Carbon  Dioxide. — Carbon  dioxide  readily  assumes 
the  solid  state  (about  one- third  of  the  whole)  on  simple  release 


CARBON  DIOXIDE  259 

of  the  liquid  to  atmospheric  pressure.  Solid  carbon  dioxide 
is  a  white,  crystalline,  snow-like  substance,  which  can  be 
handled  with  impunity  in  spite  of  its  low  temperature 
(about  —78°  C.)  if  not  pressed  too  much.  On  account  of 
its  high  latent  heat  of  vaporization,  it  may  be  kept  for  a 
considerable  period  without  special  thermal  insulation. 
Its  vapour  pressure  is  equal  to  i  atm.  at  —78*2  (Zeleny  and 
Smith,  Physik.  Zeit.,  7,  (1906),  670).  On  reducing  the 
pressure  to  2*5  mm.  the  temperature  falls  to  —130°  C. 
Mixed  with  ether  or  chloroform,  an  excellent  refrigerating 
medium  is  obtained  by  means  of  which  temperatures  as 
low  as  —85°  C.,  or  even  lower  if  the  pressure  be  reduced, 
may  be  obtained.  Its  use  also  forms  a  convenient  method 
of  maintaining  moderately  low  temperature  baths  in  the 
laboratory,  e.g.  —20  to  —50°  C.  Thus,  an  alcohol  bath 
may  be  readily  maintained  at  a  constant  temperature  in  the 
region  indicated  by  successive  additions  of  small  quantities 
of  solid  carbon  dioxide. 

MANUFACTURE  OF  CARBON  DIOXIDE 

General. — It  is  not  difficult  to  produce  carbon  dioxide 
in  a  practically  pure  state  technically,  but,  as  in  the  case  of 
sulphur  dioxide,  it  is  usually  more  economical  either  to  effect 
a  concentration  of  the  gas  from  mixtures  containing  it,  or 
to  use  it  in  the  dilute  condition. 

Consequently,  it  will  be  convenient  to  deal  separately 
with  processes  producing  pure  and  dilute  gases  respectively. 

Generation  of  Pure  Carbon  Dioxide 

(i)  Utilization  of  Natural  Sources. — Carbon  dioxide 
is  obtained  commercially  from  the  Saratoga  springs  in  New 
York,  also  from  springs  in  South  Germany  and  France.  In 
some  cases  the  gas  is  under  considerable  pressure  as  it 
issues  from  the  ground,  e.g.  15  atms. ;  the  carbon  dioxide 
is  usually  accompanied  by  a  little  sulphuretted  hydrogen. 

The  procedure  is  very  simple,  consisting  merely  in 
separating  the  gas  from  the  accompanying  water,  washing 
with  water  to  ;which  permanganate  may  be  added  in  order  to 


260  INDUSTRIAL  GASES 

remove  sulphuretted  hydrogen,  etc.,  drying  with  calcium 
chloride,  and  finally  liquefying  by  compression.  If  accom- 
panied by  nitrogen  or  air,  concentration  may  be  effected 
by  absorption  by  water  under  pressure,  with  subsequent 
disengagement  on  release  of  the  pressure,  the  water  being 
circulated  for  further  absorption  (cf.  also  the  general  dis- 
cussion of  methods  of  concentration,  p.  263). 

Carbon  dioxide  may  also  be  extracted  from  natural 
waters  containing  the  gas  in  solution  by  combined  evacua- 
tion and  steam  heating.  Although  the  gas  may  be  obtained 
in  this  way  at  low  cost,  the  cost  of  transport  makes  other 
methods  of  production  more  economical  for  places  at  a 
distance  from  the  springs. 

(2)  By  the  Thermal  Decomposition  of  Carbonates. 
— Carbonates,  such  as  calcium  carbonate,  are  fairly  easily 
decomposed  on  moderate  heating.  Thus,  the  dissociation 
pressure  of  calcium  carbonate  varies  with  the  temperature 
as  shown  by  the  following  table  (Johnson,  /.,  Amer.  Chem. 
Soc.,  32,  (1910),  938)  taken  from  a  smoothed  curve  : — 

Temperature  °C 600       650       700       750       800       850 

pcoz  (mm.  mercury)        ..          ..  2  8         25         67       170       380 

It  will  be  evident  that  a  comparatively  high  temperature, 
say  about  800°  C.,  is  necessary  for  the  rapid  expulsion  of 
the  carbon  dioxide  unless  means  are  provided  for  main- 
taining a  low  carbon  dioxide  pressure.  This  is  most  readily 
effected  by  a  current  of  steam,  as  e.g.  in  the  process  of 
Grouven  (D.R.P.  26248/83),  according  to  which  limestone 
is  heated  to  moderate  redness  in  the  upper  portion  of  vertical 
retorts  of  about  10  in.  diameter,  in  a  current  of  steam 
admitted  at  the  lower  ends  of  the  retorts.  The  steam  is 
subsequently  removed  by  condensation.  On  similar  lines 
are  the  patents  of  Thorn  and  Pryor  (B.P.s  20102/08  and 
24332/08).  Superheated  steam  is  employed,  arrangements 
being  provided  for  recuperation  of  heat ;  precautions  are 
taken  against  ingress  of  air.  Instead  of  limestone  may  be 
used  dolomite  or  magnesite,  which  have  the  advantage  of 
suffering  decomposition  at  considerably  lower  temperatures. 
It  has  been  proposed  by  Westman  (B.P.  10705/00)  to  effect 


CARBON  DIOXIDE  261 

the  decomposition  of  limestone  by  circulating  a  mixture  of 
steam  and  carbon  dioxide  through  a  heater  and  then  through 
a  shaft  containing  the  limestone,  cooling  by  injection  of 
water,  returning  to  the  pump  and  so  forth. 

(3)  By  the  Action  of  Acids  on  Carbonates.— Carbon 
dioxide  is  still  prepared  by  the  action  of  dilute  hydrochloric 
or  sulphuric  acid  on  carbonates,  such  as  limestone  (whiting), 
marble,  magnesite,  etc.,  e.g.  for  such  purposes  as  the  manu- 
facture of  artificial  mineral  waters.  Magnesite  is  often 
employed  in  Germany,  the  resulting  solution  being  worked 
up  for  magnesium  sulphate.  A  generator  for  the  pro- 
duction of  carbon  dioxide  in  this  way  consists  of  a 
lead-lined  cast-iron  or  copper  vessel  fitted  with  stirring 
gear,  acid  supply  tank,  safety  valve,  etc.  Sulphuric  acid 
is  usually  employed  in  preference  to  hydrochloric,  as  not 
giving  rise  to  volatile  impurities,  but  has  the  disadvantage 
of  yielding  an  insoluble  sludge  with  calcium  carbonate. 
In  both  cases  it  is  important  that  the  acid  should  be 
free  from  arsenic.  Marble  often  contains  organic  matter. 
Sodium  bicarbonate  is  sometimes  employed,  giving  a  very 
pure  but  very  expensive  gas.  L,ead  is  always  liable  to 
be  present  and  the  use  of  such  generators  has  been  largely 
superseded  by  the  cheap  and  pure  liquid  carbon  dioxide. 
If  desired  the  apparatus  may  be  adapted  to  produce  the 
carbon  dioxide  under  the  pressure  required  for  the  saturation 
of  the  mineral  waters,  by  the  employment  of  an  acid  reservoir 
the  top  of  which  is  connected  to  the  gas  exit  of  the  generator. 
The  gas  leaving  the  generator  is  freed  from  acid  spray  by 
scrubbing  with  water,  which  may  be  distributed  on  lumps 
of  marble  or  limestone,  Organic  compounds  and  sulphur- 
etted hydrogen  may  be  removed  by  washing  with  per- 
manganate solution,  while  complete  elimination  of  acid 
spray  is  sometimes  ensured  by  washing  with  sodium  bicar- 
bonate solution.  When  the  gas  is  being  generated  with 
sulphuric  acid,  permanganate  may  be  added  directly  to  the 
generator. 

In  order  to  avoid  the  use  of  sulphuric  acid,  proposals  have 
been  made  by  Mackey  and  Carrol  (B.P.  109511/16)  to  treat 


262  INDUSTRIAL  GASES 

calcium  carbonate  with  a  solution  of  nitre  cake  (the  NaHSO4 
and  Na2SO4  mixture  resulting  as  a  waste  product  in  the 
manufacture  of  nitric  acid  from  Chile  saltpetre),  use  being 
made  of  the  mixture  of  calcium  and  sodium  sulphates 
produced,  for  glass  manufacture,  etc. 

A  cyclic  process  has  been  proposed  by  Howard  (D.R.P. 
132623/00)  in  the  production  of  bisulphite  by  the  action  of 
sulphur  dioxide  (burner  gases)  on  sodium  sulphite  solution, 
half  of  the  resulting  bisulphite  solution  to  be  used  to  generate 
carbon  dioxide  by  interaction  with  hot  sodium  carbonate 
solution — 

Na2C03  +  2NaHS03  =  2Na2SO3  +  H2O  +  CO2 

The  sodium  sulphite  solution  is  re-treated  with  sulphur 
dioxide,  half  of  it  being  returned  to  the  cycle  while  the 
remainder  is  marketed ;  the  carbon  dioxide  is  cooled  and 
washed  with  sodium  carbonate  solution. 

According  to  Behrens  (D.R.P.  305417/17)  neutral  or 
basic  carbonates  are  decomposed  by  heating  with  water 
under  pressure  to  150°  C.  or  over. 

(4)  Production  of  Carbon  Dioxide  as  a  By-product 
in  Fermentation  Processes. — Carbon  dioxide  is  produced  in 
enormous  quantities  by  alcoholic  fermentation  in  the  manu- 
facture of  beer,  etc.     According  to  Goosmann,  i  Ib.  of  carbon 
dioxide  results  from  each  5-6  gallons  of  wort.     As  a  rule, 
the  gas  is  allowed  to  escape,  but  in  some  cases  is  collected. 
If  the  gas  be  drawn  from  the  vats  without  access  of   air 
the  treatment  is  simple  and  direct  compression  may  be 
performed.     If,  on  the  other  hand,  the  carbon  dioxide  is 
obtained  only  in  the  dilute  state,  concentration  must  be 
effected  before  liquefaction  by  one  or  other  of  the  methods 
described  below.     The  carbon  dioxide  obtained  in  this  way 
has  an  odour  of  fusel  oil,  which  is  not  detrimental  if  the  gas 
is  to  be  used  for  beer  raising  ;  if  for  other  purposes  purifica- 
tion  by   permanganate    solution,    sulphuric    acid,    etc.,    is 
necessary. 

(5)  Other  Methods  for  the  Production  of  Carbon 
Dioxide. — Among  other  methods  of  producing  pure  carbon 


CARBON  DIOXIDE  263 

dioxide  may  be  mentioned  that  due  to  Wallace  and  Ball  (B.P. 
24652/94 — cf.  also  Lane  and  Pullman,  D.R.P.  77150/93). 
In  this  cyclic  process,  air  is  passed  first  through  a  retort 
containing  coke  whereby  carbon  monoxide  is  generated,  and 
then  through  a  second  retort  charged  with  copper  oxide. 
Carbon  dioxide  is  thus  formed  and  reaching  again  the  coke 
retort,  each  volume  produces  two  volumes  of  carbon  mon 
oxide,  which  in  turn  give  two  volumes  of  carbon  dioxide — 

CO  ->  C02  ->  2CO  ->  2C02 

one  of  which  is  retained  in  the  cycle  while  the  other  is 
removed  to  a  gas-holder.  Nitrogen  is  eliminated  by  passing 
the  first  portions  to  waste,  or  alternatively  the  apparatus 
may  be  filled  with  carbon  dioxide  at  the  outset. 

Concentration  of  Carbon  Dioxide  from  Mixtures 
with  other  Gases 

(i)  By  means  of  Water  under  Pressure. — Reference 
has  already  been  made  under  the  manufacture  of  hydrogen,  to 
the  removal  of  carbon  dioxide  :  (a)  from  water  gas  which  has 
been  passed  over  a  heated  catalyst  and  contains  some  30  % 
carbon  dioxide,  in  the  B.A.M.A.G.  continuous  catalytic  pro- 
cess (p.  159)  ;  (b)  from  blue  water  gas  containing  some  5  % 
carbon  dioxide,  as  a  preliminary  to  fractionation  in  the 
Ivinde-Frank-Caro  process  (p.  172).  Although  the  recovery 
of  carbon  dioxide  is  not  necessarily  carried  out,  it  is  easily 
realized  on  the  release  of  the  water  from  the  scrubber, 
when  most  of  the  carbon  dioxide  is  disengaged,  accompanied 
by  some  sulphuretted  hydrogen  together  with  small  quanti- 
ties of  nitrogen,  hydrogen,  carbon  monoxide,  etc.  The 
utilization  of  such  carbon  dioxide  for  the  production  of 
ammonium  carbonate,  cf.  B.P.s  of  the  Badische  Co.  23939/14 
and  24042/14,  when  the  hydrogen  is  being  produced  by  the 
continuous  catalytic  process  for  the  synthetic  manufacture 
of  ammonia,  is  interesting,  the  quantity  of  carbon  dioxide 
being  more  than  sufficient  for  the  saturation  of  the  ammonia 
simultaneously  produced  (cf.  p.  215).  Another  similar 
process  consists  in  the  preliminary  production  of  ammonium 


264  INDUSTRIAL  GASES 

carbonate  and  conversion  into  ammonium  sulphate  by 
interaction  with  gypsum,  thus  avoiding  the  use  of  sulphuric 
acid  (Badische  Co.,  B.P.  27962/13). 

For  other  references  to  this  subject  cf.  "  Purification  of 
Hydrogen,"  p.  207. 

(2)  By  the  Alternate  Formation  and  Decomposition 
of  Alkali  Bicarbonates  in  Solution. — Some  reference  to  the 
use  of  ammonium  hydroxide  and  of  sodium  and  potassium 
carbonates  for  this  purpose  has  been  made  on  p.  210.     In 
the  Glaus  process  (q.v.)  ammoniacal  liquor  is  used,  carbon 
dioxide   being   subsequently  expelled  without  noteworthy 
loss  of  ammonia  by  heating  to  about  90°  C.    The  process 
most  generally  used,  however,  is  that  depending  on  the  use 
of  sodium  or  potassium  carbonate  solutions.     In  view  of 
its  greater   solubility    and   consequent   greater   absorptive 
power,   potassium  carbonate  is  usually  employed  in  pre- 
ference to  the  corresponding  sodium  salt.     An  important 
consideration  in  the  economics  of  such  a  process  lies  in  the 
proper  recuperation  of  the  large  quantities  of  heat  involved 
in  changing  the  temperature  of  the  liquor  passing  round  the 
cycle.     In  order  to  avoid  this  troublesome  point  the  lye 
may  be  maintained  at  constant  temperature  and  the  dis- 
sociation controlled  by  variation  of  pressure.     Since,  how- 
ever,  the  exact  procedure  is  largely   conditioned  by  the 
particular  method  of  obtaining  the  dilute  carbon  dioxide, 
further  details  will  be  given  under  the  different  processes. 

(3)  By  Liquefaction. — According  to  Leslie  (B.P.  11902/06) 
cf.  also  Windhausen,  D.R.P.  45102/87,   carbon  dioxide  is 
separated  from  furnace  gases  by  compressing,  drying,  and 
subsequently  cooling  the  gases  to  a  low  temperature.     The 
carbon  dioxide  separates  out  in  the  liquid  state  while  the 
other  gases  pass  out  through  a  heat-interchanger.     Reference 
to  p.  258  will  indicate  the  partial  pressures  of  carbon  dioxide 
which  must  be  attained  before  any  liquefaction  can  ensue. 

Production  and  Concentration  of  Dilute  Carbon 
Dioxide  from  Products  of  Combustion. — Attention  has 
already  been  paid,  under  the  manufacture  of  nitrogen,  to  the 
production  of  a  mixture  of  carbon  dioxide  and  nitrogen  free 


CARBON  DIOXIDE  265 

from  carbon  monoxide,  hydrogen  and  oxygen.  For  some  uses 
further  treatment  is  unnecessary,  but  when  pure  carbon 
dioxide  is  required  for  purposes  of  liquefaction,  etc.,  a 
process  somewhat  as  follows  is  adopted,  depending  on  the 
cyclic  alkali  bicarbonate  system  proposed  by  Ozouf  in  1865, 
and  first  applied  technically  by  I/uhmann. 

The  starting  material  is  usually  coke,  which  is  burnt  with 
a  mechanical  stoker  or  with  other  precautions  to  ensure 
regular  combustion  with  the  minimum  excess  of  air,  or 
alternatively  first  gasified  in  a  producer,  the  resulting  air 
producer  gas  being  burnt  with  a  secondary  air  supply  in  a 
combustion  chamber  (cf.  Schmalotta,  Z.  angew.  Chem., 
(1900),  1284).  In  the  former  case  secondary  air  may  be 
admitted  behind  the  bridge  of  the  fire-box  to  remove  any 
hydrogen,  carbon  monoxide,  and  sulphuretted  hydrogen. 
The  complete  conversion  of  the  last  mentioned  impurity 
to  sulphur  dioxide  is  particularly  important  since  it  would 
otherwise  accumulate  in  the  potash  lye  with  deleterious 
effect.  In  either  case  the  heat  of  combustion  is  employed 
for  heating  a  boiler  containing  potash  lye,  to  which  plant  we 
shall  have  occasion  to  refer  presently.  Theoretically,  with 
just  sufficient  oxygen  for  complete  combustion,  the  carbon 
dioxide  content  of  the  flue  gases  should  be  some  20  %  ; 
in  practice  about  16  %  is  realized.  After  passing  through  a 
water  scrubber,  where  dust  and  sulphur  dioxide  are  removed 
and  which  may  be  packed  with  lumps  of  limestone,  the 
temperature  of  the  washing  water  being  about  40°  C.,  the 
cleansed  and  cooled  gases  enter  the  absorber  which  may 
take  the  form  of  a  coke  tower,  a  suitable  capacity  of  which 
is  some  10  ft3./lb.  carbon  dioxide/hour  according  to  Goos- 
mann,  or  of  chambers  fitted  with  baffles  and  dashers  or  of 
such  chambers  followed  by  a  tower.  Counter-current 
scrubbing  with  potassium  carbonate  solution,  usually  con- 
taining about  15-20  grams  K2CO3/ioo  grams  solution,  is 
carried  out,  the  temperature  of  the  liquor  being  about 
30-40°  C.  Only  about  half  the  carbon  dioxide  is  absorbed, 
the  exact  amount  depending  on  the  efficiency  of  the  absorp- 
tion arrangements,  the  rest  passing  to  waste  with  the  nitrogen 


268  INDUSTRIAL  GASES 

which  it  is  heated  ;  the  spent  lye  flows  back  through  the 
second  heat-interchanger  and  a  cooler  to  the  absorber. 

The  Production  and  Transport  of  Liquid  Carbon 
Dioxide. — Before  liquefaction,  carbon  dioxide  must  be 
dried  thoroughly,  and  this  is  usually  accomplished  by  passing 
the  gas  through  drying  chambers  packed  with  granular 
calcium  chloride,  either  at  the  ordinary  pressure  or  after 
the  first  stage  of  compression.  In  order  to  avoid  intro- 
duction of  moisture  in  the  second  or  further  stages  of  the 
compression,  glycerol  may  be  used  for  the  internal  lubrication 
of  the  pump,  being  subsequently  separated.  A  balancing 
gas-holder  is  used  before  the  compressor  and  should  be  of 
the  annular  water-channel  type  in  order  to  minimize  loss 
of  carbon  dioxide  by  solution. 

lyiquid  carbon  dioxide  is  transported  in  cylinders  which 
may  hold  about  25  or  66  Ibs.  On  account  of  its  very  high 
coefficient  of  expansion,  great  care  must  be  taken  in  filling 
the  cylinders  to  ensure  that  the  proper  charge  is  not  ex- 
ceeded and  that  the  cylinder  shall  not  be  exposed  to  the 
sun  or  hot  situations. 

The  question  of  the  degree  of  filling  is  discussed  very 
fully  by  Stewart  (see  p.  44),  who  recommends  a  filling  of 
62  %  by  weight  of  the  water  capacity  or  38-8  Ibs.  carbon 
dioxide  per  ft.3  of  cy Under  space,  assuming  a  maximum 
possible  temperature  of  49°  C. 

The  recommendations  of  the  British  Parliamentary 
Committee  on  the  Manufacture  of  Compressed  Gas  Cylinders 
(1895)  are  that  the  maximum  charge  shall  be  47  lbs./ft.3  for 
this  country  and  41*7  lbs./ft.3  for  the  tropics,  while  a  test 
pressure  of  224  atms.  is  specified.  The  German  railway 
regulation  of  i  kilo. /i -34  litres  corresponds  with  the  higher 
figure.  Absence  of  air  in  the  cylinders  is  important  since 
each  per  cent,  of  air  involves  an  increase  in  pressure  of  the 
order  of  4-5  atms.  at  temperatures  between  40°  and  60°  C. 

The  Production  and  Transport  of  Solid  Carbon 
Dioxide. — In  order  to  avoid  the  inconvenience  of  handling 
and  the  expense  of  transport  of  cylinders,  the  weight  of  which 
is  of  the  order  of  five  times  that  of  the  liquid  carbon  dioxide 


CARBON  DIOXIDE  269 

itself,  the  substance  is  sometimes  sent  from  tne  works  in 
the  solid  state*  for  use  when  consumption  is  to  be  more  or  less 
immediate  and  the  distance  of  transport  is  relatively  small. 
The  carbon  dioxide  snow  is  compressed  in  wooden  moulds. 

Applications  of  Carbon  Dioxide 

(a)  In  the  Solvay  Ammonia-soda  and  the  Claus- 
Chance  Sulphur  Recovery  Processes. — One  of  the  most 
important  applications  of  carbon  dioxide  is  in  connection  with 
the  manufacture  of  sodium  carbonate,  both  by  the  old  I,eblanc 
process  and   by  the  newer   ammonia-soda  Solvay  process. 
We  will  deal  first  with  the  latter  process.     The  dilute  carbon 
dioxide  gases,  from  special  kilns  and  containing  some  30  % 
carbon    dioxide,    are    used    without    concentration.     The 
process   consists  in  the   double   decomposition   of  sodium 
chloride  and   ammonium  bicarbonate  with  the  production 
of  ammonium  chloride  and  sodium  bicarbonate.     Ammonia 
is  first  passed  into  saturated  brine  and  the  solution  then 
saturated  with  carbon  dioxide  in  a  tower  or  other  absorber 
at   a   temperature   of    25-30°   C.     With  the   high   towers 
which  are   often  employed,  the  hydrostatic  head  of  brine 
may  cause  a  pressure  of  some  2  atms.  on  the  gases  entering 
at  the  bottom.     Conditions  are  so  adjusted  that  the  sparingly 
soluble  sodium  bicarbonate  separates  out ;   the  ammonia  is 
recovered  from  the   solution  by   boiling  with  lime.     The 
bicarbonate    is     decomposed    by    calcination,    the     gases, 
containing  in  practice   some  50  %   carbon   dioxide,  being 
collected  and  returned  to  the  cycle. 

The  Glaus-Chance  process  has  been  used  to  some  extent 
in  connection  with  the  L,eblanc  process  and  consists  in  the 
recovery  of  the  sulphur  from  the  "  vat  waste  "  (mostly 
calcium  sulphide)  by  treatment  while  suspended  in  water 
with  gases  containing  carbon  dioxide,  when  calcium  carbonate 
and  sulphuretted  hydrogen  result. 

(b)  In  the  Manufacture  of  Artificial  Mineral  Waters. 

*  Solid  carbon  dioxide  is  conveniently  prepared  in  the  laboratory  by 
tilting  a  cylinder  so  that  the  valve  delivers  liquid,  binding  a  canvas  bag 
over  the  aperture  and  releasing  the  liquid,  preferably  in  a  series  of  jerks. 


266  INDUSTRIAL  GASES 

and  oxygen.  The  saturated  lye  now  passes  to  the  boiler 
through  a  heat-interchanger  in  counter-current  to  the  hot 
lye  leaving  the  same.  This  boiler,  as  stated  above,  is  heated, 
to  a  little  above  100°  C.,  by  the  combustion  from  which  the 
carbon  dioxide  results.  After  giving  up  its  carbon  dioxide, 
the  hot  spent  lye  is  taken  first  to  the  heat-interchanger  and 
then  through  a  cooler  to  the  absorber  again.  The  moist 
carbon  dioxide  leaving  the  boiler  is  cooled  by  a  system  of 
coils  traversed  by  water,  the  condensed  moisture  being 
returned  to  the  boiler.  The  heat  of  condensation  of  the 
steam  may  also  be  utilized  for  heating  up  the  saturated  lye. 

Instead  of  using  potassium  carbonate,  it  is  possible  to 
operate  with  a  solution  of  sodium  carbonate  containing  e.g. 
6  grams  Na2CO3/ioo  grams  solution,  but  the  results  are 
less  favourable.  Further,  as  in  the  Stirth  process  (vide 
infra),  the  variation  in  the  carbon  dioxide  content  of  the 
lye  may  be  produced  by  alteration  of  pressure  at  constant 
temperature.  It  has  been  found  that  the  addition  of  froth- 
producing  substances,  such  as  soap,  is  beneficial  both  as 
regards  the  absorption  and  the  disengagement  of  the  carbon 
dioxide.  According  to  some  systems,  producer  gas  is  used, 
part  being  burnt  under  the  lye  boiler  and  part  in  a  gas 
engine  providing  the  necessary  power,  the  carbon  dioxide 
from  both  combustions  being  utilized. 

Carbon  dioxide  produced  by  concentration  in  this  way 
has  usually  a  high  degree  of  purity. 

Siirth  System. — In  this  instance  the  exhaust  gases  from 
an  internal  combustion  engine  are  used  as  a  source  of 
carbon  dioxide,  the  engine  providing  the  power  required 
for  the  concentration  process.  Working  in  this  way,  the 
combustion  is  under  exact  control.  Using  suction  gas 
e.g.  of  the  percentage  composition — 

Hydrogen       . .  . .  . .  15*0 

Carbon  monoxide  . .  . .  27*0 

Carbon  dioxide  . .  . .  5*5 

Methane         . .  . .  . .  0*5 

Nitrogen         . .  . .  . .  52*0 


CARBON  DIOXIDE  267 

and  diluting  with  air  to,  say  30  C.H.U.  net  calorific  value 
per  ft.3  (cf.  p.  346),  the  percentage  of  carbon  dioxide  in  the 
water-free  product  would  be  some  16  %.  The  sensible  heat 
of  the  exhaust  gas  is  utilized  by  passage  through  a  boiler  in 
which  the  saturated  lye  is  heated ;  the  cooled  gases,  after 
traversing  a  scrubber,  are  compressed  to  about  5  atms.  and 
enter  the^  absorber  which  is  fed  with  potash  lye  at  about 
100°  C.  As  the  lye  leaves  the  absorber,  its  pressure  is 
released  to  atmospheric,  and  on  entering  the  boiler  carbon 
dioxide  is  disengaged.  No  heat-interchangers  are  used,  and 
apart  from  losses,  no  temperature  changes  occur  in  the  lye. 
It  is  stated  that  a  fuel  consumption  of  J  to  f  Ib.  coke  per  Ib. 
carbon  dioxide  produced  is  sufficient. 

Production  and  Concentration  of  Dilute  Carbon 
Dioxide  from  Lime-kiln  Gases. — This  method  of  manufac- 
ture of  dilute  carbon  dioxide  is  usually  employed  in  connection 
with  the  manufacture  of  sodium  carbonate  by  the  "  ammonia- 
soda  "  process.  For  this  purpose  it  is  advisable  that  the 
concentration  of  carbon  dioxide  in  the  gases  should  not  fall 
below  30  %,  consequently  the  kilns  are  made  very  large.  In 
order  to  effect  fuel  economy  the  kilns  are  generally  internally 
fired  by  coke  mixed  with  the  limestone,  usually  in  the 
proportion  of  about  i  :  7,  the  carbon  dioxide  from  the 
combustion  being  also  utilized.  In  some  cases,  however, 
the  kiln  is  heated  by  gas  from  a  separate  coke  producer,  the 
gas  being  burnt  in  the  kiln  by  the  admission  of  secondary  air. 
When  required  for  use  in  the  dilute  state  the  gas  is  freed  from 
dust  in  a  plate  washer  or  in  a  coke  scrubber.  The  use  of 
magnesite  results  in  a  higher  carbon  dioxide  concentration 
on  account  of  the  lower  decomposition  temperature  of  this 
carbonate  as  compared  with  limestone. 

In  order  to  effect  concentration  of  the  gases,  similar  arrange- 
ments to  those  for  dealing  with  products  of  combustion  are 
usually  adopted.  The  kiln  gases  pass  through  a  heat-inter- 
changer  to  a  coke  scrubber  and  then  to  the  absorption  towers. 
The  saturated  lye  traverses  a  second  heat-interchanger  in 
counter-current  to  the  lye  leaving  the  boiler  and  then  passes 
through  the  heat-interchanger  mentioned  above  to  a  boiler  in 


270  INDUSTRIAL  GASES 

— In  this  important  application  of  carbon  dioxide  the  pure 
gas  is  required,  and,  for  reasons  to  which  reference  has  been 
made,  liquid  carbon  dioxide  is  now  usually  employed  in 
preference  to  the  gas  generated  by  the  action  of  acids  on 
carbonates.  The  gas  is  generally  taken  from  a  gas-holder 
and  forced  by  a  pump  into  a  saturator  vessel  of  gun  metal 
lined  with  tin,  into  which  water  is  also  pumped  at  the  same 
time. 

Any  required  additions  such  as  sodium  carbonate, 
syrups,  etc.,  are  made  to  the  individual  bottles  which  are 
then  rilled  with  the  water  saturated  with  carbon  dioxide  at 
the  prescribed  pressure,  means  being  provided  for  the 
escape  of  air.  Complete  expulsion  of  air  is  important  since 
its  presence  causes  the  mineral  waters  to  become  "  flat  " 
rapidly  on  opening.  According  to  Mitchell  (Thorpe's 
"  Dictionary  of  Applied  Chemistry,"  1912)  the  actual 
pressure  in  unsweetened  mineral  water  bottles  is  usually 
45-55  lbs./in.2  corresponding  to  a  bottling  pressure  of 
120  lbs./in.2.  In  the  case  of  lemonade  and  the  like  the 
water  is  saturated  at  only  about  60-80  lbs./in.2.  Soda 
water  siphons  are  bottled  at  a  pressure  of  150  lbs./in.2. 

(c)  In  Refrigeration  Plant. — Carbon  dioxide  is  exten- 
sively used  in  refrigeration  plant,  especially  on  board  ship  ; 
the  chief  advantages  in  comparison  with  ammonia,  which 
gives  a  somewhat  more  efficient  cycle  for  normal  refrigeration 
temperatures,  are  the  small  dimensions  of  the  compressor, 
the  relative  absence  of  danger  and  nuisance  from  leakages, 
the  use  of  copper  tubing  and  the  smaller  cost  of  the  carbon 
dioxide.     Carbon  dioxide  plants  are  capable  of    working 
efficiently  to  a  lower  temperature  than  ammonia  plants. 
The  small  sized    compressors  are  generally  constructed  of 
bronze.     In  view  of  the  high  working  pressure,  the  glands 
on  the  cylinders  are  usually  sealed  with  oil  maintained  at  a 
pressure  slightly  higher  than  that  of  the  gas,  leakage  being 
thus  entirely  eliminated  at  these  points. 

(d)  Other  Applications  of  Carbon  Dioxide.— Among 
the  many  uses  of  carbon   dioxide   may  be  mentioned  the 
following. 


CARBON  DIOXIDE  271 

The  use  of  carbon  dioxide  for  the  compression  of  fluid  steel 
in  the  ingot  moulds  was  introduced  by  Messrs.  Krupp,  the 
liquid  carbon  dioxide  serving  as  a  convenient  means  of 
generating  enormous  pressures. 

Experiments  have  been  carried  out  recently  (cf.  J.  Soc. 
Chem.  Ind.,  (1918),  224  R)  on  the  use  of  carbon  dioxide  for 
the  destruction  of  pests  In  grain  by  forcing  the  gas  into  the 
air-tight  silos  in  which  the  grain  is  stored ;  some  14  ft.3  of 
carbon  dioxide  are  sufficient  for  the  submersion  of  i  ton  of 
grain.  According  to  Dendy  (Nature,  103,  (1919),  55)  air  con- 
taining 20  %  carbon  dioxide  is  more  effective  than  pure 
carbon  dioxide,  the  spontaneous  accumulation  of  carbon 
dioxide  in  an  air-tight  silo  being  sufficient. 

Carbon  dioxide  is  employed  for  fire  extinction,  usually 
in  the  form  of  an  aqueous  solution  produced  when  required 
by  the  action  of  sulphuric  acid  on  an  excess  of  sodium 
carbonate  solution  in  a  special  generator. 

Iviquid  carbon  dioxide  has  been  applied  as  a  source  of 
motive  power  for  torpedoes  and  the  like  ;  for  operating 
pneumatic  railway  signals  in  outlying  districts,  thus  avoiding 
the  transmission  of  compressed  air  over  long  distances ;  for 
refloating  sunken  ships,  etc.  lyiquid  carbon  dioxide  is  also 
used  extensively  for  carbonating,  clarifying  and  raising 
beer.  In  the  raising  operation,  the  cylinder  is  fitted  with  a 
reducing  valve,  the  low  pressure  side  being  connected  to 
the  barrel,  keeping  the  beer  saturated  with  carbon  dioxide 
in  addition  to  avoiding  the  necessity  for  pumping.  Other 
applications  are  the  protecting  of  wines  from  moulds ;  the 
synthetic  production  of  salicylic  acid  from  phenol  (Chem. 
Trade  /.,  62,  (1918),  337)  ;  the  manufacture  of  white 
lead ;  the  decomposition  of  calcium  or  strontium  sugar 
compounds  in  sugar  refining  ;  the  precipitation  of  pure 
alumina  from  sodium  aluminate  solutions  produced  from 
bauxite  or  cryolite,  pure  alumina  being  precipitated  and 
sodium  carbonate  remaining  in  solution  ;  the  manufacture 
of  bread  ;  the  production  of  carbonates,  etc. 

An  interesting  application  of  carbon  dioxide  is  in  the 
production  of  formates  by  interaction  with  hydrogen  in  the 


272  INDUSTRIAL   GASES 

presence  of  a  catalyst  (cf.  Bredig  and  Carter,  B.P.  801/15, 
also  Ber.,  47,  (1914),  541  ;  Chem.  Zeit.,  39,  (1915),  72). 
According  to  these  authors  potassium  formate  may  be 
produced  by  vigorous  agitation  of  a  5  %  aqueous  solution  of 
potassium  bicarbonate  containing  some  0*75  %  by  weight 
of  platinum  black,  with  hydrogen  at  a  pressure  of  60  atms. 
and  at  a  temperature  of  70°  C.  For  the  apparatus  used  in  the 
early  investigations  see  Stuckert  and  Enderli,  Z.  Elektrochem., 
19,  (1913),  570.  Under  these  conditions  a  20  %  yield  of 
formate  is  obtained.  The  same  effect  is  produced  by 
treating  a  solution  of  borax  with  carbon  dioxide  and  hydrogen 
simultaneously  or,  alternatively,  calcium  carbonate  may  be 
treated  with  hydrogen  in  the  presence  of  platinum  black 
with  the  production  of  calcium  formate.  B.P.  9762/15 
relates  to  the  production  of  the  free  acid  by  the  interaction 
of  water,  hydrogen  and  carbon  dioxide.  A  similar  com- 
bination may  be  induced  by  the  action  of  sodium  amalgam 
on  an  aqueous  solution  of  carbon  dioxide  (cf.  Waygouny, 
/.  Soc.  Chem.  Ind.,  (1916),  736  ;  Kolbe  and  Schmidt,  Liebig's 
Annalen,  119,  (1861),  251). 

Carbon  dioxide  has  some  antiseptic  properties  and  is 
used  for  the  sterilization  of  milk  and  organic  liquids.  It  is 
used  therapeutically  for  baths  either  in  presence  or  absence 
of  water  vapour,  its  action  being  to  induce  perspiration ; 
also  in  aqueous  solution.  The  gas  is  used  for  the  destruction 
of  vermin,  such  as  rats,  etc.  On  mixing  carbon  dioxide 
to  the  extent  of  5-8  %  with  acetylene,  the  smoky  character 
of  the  flame  is  lessened. 

Estimation  and  Testing  of  Carbon  Dioxide.— Carbon 
dioxide  is  perhaps  the  easiest  of  all  gases  to  estimate.  When 
present  in  small  quantities  it  is  readily  recognized  by  its 
action  on  lime-water  or  baryta  solution.  It  is  usually 
estimated  by  absorption  in  caustic  soda  solution.  In  very 
small  amount,  e.g.  as  in  the  air,  it  may  be  determined  by 
passing  through  excess  standard  baryta  solution  and  titrating 
back  with  oxalic  acid,  using  phenolphthalein  as  indicator. 
One  of  the  chief  needs  for  estimating  carbon  dioxide  is  in 
connection  with  flue  gases,  and  many  forms  of  automatic 


CARBON  DIOXIDE  273 

apparatus  depending  both  on  absorption  with  caustic  soda 
and  also  on  physical  methods  (cf.  p.  33)  have  been  devised 
for  this  purpose.  Space  will  not  permit  of  a  full  description 
of  these  methods  here,  but  reference  may  be  made  to  lounge's 
"  Technical  Gas  Analysis,"  1914. 

Commercial  liquid  carbon  dioxide  is  examined  by  with- 
drawing a  sample  of  gas  from  the  inverted  bottle.  The 
content  of  permanent  gases  (air,  carbon  monoxide,  etc.)  is 
found  by  absorption  of  the  carbon  dioxide  by  alkali.  An 
approximate  estimate  of  the  air  content  of  a  cylinder  may 
be  obtained  by  determining  the  air  contents  of  the  first  and 
last  portions  of  the  gas  delivered  from  the  upright  cylinder 
(lounge,  loc.  cit.}.  According  to  Werder  (Chem.  Zeit.,  (1906), 
1021)  the  absence  of  empyreumatic  substances  may  be 
judged  by  the  smell  and  taste  ;  at  least  98  %  of  the  gas 
should  be  absorbed  by  alkali ;  the  carbon  monoxide  content 
should  not  exceed  0-5  %  ;  the  gas  should  be  free  from  sulphur 
dioxide  and  oxides  of  nitrogen,  and  should  not  decolorize 
potassium  permanganate  solution  or  give  a  precipitate  with 
silver  nitrate  solution. 


REFERENCES   TO  SECTION  IX. 

Goosman,  "  The  Carbonic  Acid  Industry."     Chicago,  1907. 

Kausch,  "  Die  Kohlensaure,  ihre  Herstellung  und  Verwendung." 
Hanover,  1909. 

Thorpe,  "A  Dictionary  of  Applied  Chemistry."  London,  1912.  Articles 
on  "  Carbon  Dioxide  "  and  "  Mineral  Waters." 

Lunge,  "  Sulphuric  Acid  and  Alkali,"  vol.  iii.  London,  Third  Edition, 
1911. 

Stewart,  "  The  Physical  Properties  of  Carbonic  Acid  and  the  Conditions 
of  its  Economic  Storage  for  Transportation,"  Trans.  Amer.  Soc.  Mech. 
Eng.,  30  (1908),  mi. 


A.  18 


SECTION  X.— SULPHUR   DIOXIDE 

Properties  of  Sulphur  Dioxide. — Sulphur  dioxide  is  a 
colourless  gas  with  a  very  characteristic  and  pungent  odour. 
It  occurs  in  volcanic  gases  and  in  very  small  traces  in  town 
air,  being  chiefly  derived  from  the  iron  pyrites  present  in 
coal.  The  chief  physical  properties  of  this  easily  liquefiable 
gas  will  be  found  in  Tables  12  and  13,  pp.  53-6. 

vSulphur  dioxide  dissolves  in  water  to  a  considerable 
extent  with  evolution  of  heat,  the  solubility  amounting  to 
47*3  volumes  of  gas  measured  at  N.T.P.,  at  15°  C.  and 
I  atm.  pressure,  including  water  vapour,  equivalent  to  12*16  % 
by  weight.  Other  values  are  given  in  the  following  table  : — 

Temperature  °C. ..          ..          ..         o         10         15         20         30         40 

C.c.  of  gas  (measured  at  N.T.P.)) 

dissolved  by  I    c.c.  of   water!  7g.$      56-6     4?-3      39-4      27>2      lg.g 

under  a  pressure  of  i  atm.  in-j 

elusive  of  water  vapour  J 

Solid  hydrates  are  formed  with  water  under  suitable 
conditions,  9-15  molecules  of  water  being  linked  up.  The 
aqueous  solutions  decompose  very  slowly  at  the  ordinary 
temperature  with  the  final  production  of  sulphur  and  sul- 
phuric acid,  the  action  being  rapid  in  sealed  tubes  above 
160°  C.  (Jungfleisch  and  Brunei,  Comptes  Rend.,  156, 
(1913),  1719).  The  gas  is  soluble  to  a  considerable  extent 
in  sulphuric  acid,  one  volume  of  which  dissolves  about  58 
volumes  of  sulphur  dioxide  at  ordinary  temperatures ;  it 
is  also  dissolved  by  mineral  oils,  the  solutions,  if  dry,  having 
no  action  on  metals. 

According  to  von  Wartenberg  (Z.  anorg.  Chem.,  56, 
(1908),  320)  sulphur  dioxide  undergoes  no  appreciable 
dissociation  at  2200°  absolute  ;  cf.  also  Ferguson,  /.  Amer. 
Chem.  Soc.t  41,  (19*9),  69.  A  slight  decomposition  takes 


SULPHUR  DIOXIDE  275 

place  at  tlie  ordinary  temperature  under  the  influence  of 
light,  sulphur  and  sulphur  trioxide  being  produced. 

The  most  characteristic  chemical  property  of  sulphur 
dioxide  is  its  action  as  a  reducing  agent,  itself  suffering 
oxidation  to  sulphuric  acid ;  thus  potassium  dichr ornate  is 
reduced  to  chromic  sulphate.  In  some  cases,  however,  it 
behaves  as  an  oxidizing  agent,  thus  Smythe  and  Wardlaw 
(/.  Soc.  Chem.  Ind.,  (1915),  797)  found  that  titanium 
trichloride  and  stannous  chloride  were  oxidized  by  sulphur 
dioxide  in  warm,  strongly  acid  solution  ;  the  intermediate 
formation  of  thionyl  chloride  is  suggested  as  an  explanation. 

Sulphur  dioxide  has  an  irritating  action  on  the  mucous 
membrane ;  according  to  the  Selby  Smelter  Commission 
(U.S.  Bureau  of  Mines,  Bull.  No.  98),  0^0005%  sulphur  dioxide 
can  be  detected  by  smell,  while  0*05  %  is  practically  un- 
endurable. A  concentration  greater  than  0*003  %  is 
injurious  to  vegetation  (lyunge). 

When  dry,  sulphur  dioxide  has  no  action  on  iron  even  at 
100°  C.,  but  in  the  presence  of  moisture  a  slight  action  is 
observed  (cf.  L,ange,  Z.  angew.  Chem.,  12,  (1899),  275,  303, 
595).  As  liquid  sulphur  dioxide  cannot  contain  more  than 
about  i  %  moisture  at  the  ordinary  temperature,  the  action 
is  slight,  but  in  sulphur  dioxide  refrigeration  plants,  where 
a  considerable  temperature  rise  occurs  in  the  compression,  the 
action  becomes  of  importance.  liquid  sulphur  dioxide  is 
miscible  in  all  proportions  with  sulphuric  anhydride,  but 
immiscible  with  sulphuric  acid. 

Sulphur  dioxide  may  be  obtained  in  the  solid  state  by 
evaporation  of  the  liquid  under  reduced  pressure. 

MANUFACTURE  OF  SULPHUR  DIOXIDE 

General. — The  manufacture  of  sulphur  dioxide  in  the 
pure  state  is,  in  most  cases,  a  question  of  concentration  of 
the  more  or  less  dilute  gases  obtained  in  various  ways. 
Although  the  only  process  which  appears  to  be  in  use  at 
the  present  time  is  that  of  Hanisch  and  Schroder  (see  below), 
it  will  be  well  to  consider  briefly  some  other  methods  which 
have  been  worked  or  proposed.  One  of  the  earliest  used 


276  INDUSTRIAL   GASES 

was  the  Melsens-Pictet  method,  depending  on  the  action  of 
concentrated  sulphuric  acid  when  dropped  into  molten 
sulphur  at  a  temperature  of  400°  C.  This  process  was 
used  by  certain  French  firms.  The  moist  sulphur  dioxide 
was  compressed  and  cooled  to  about  — 10°  C.  when  the  gas 
liquefied ;  any  water  present  served  to  produce  hydrates, 
sufficiently  stable  to  allow  of  all  the  sulphur  dioxide  being 
subsequently  pumped  off  (D.R.P.  22365/82).  One  dis- 
advantage of  this  method  of  generating  sulphur  dioxide  is 
the  action  of  the  sulphur  on  the  iron  retort,  and  an  improve- 
ment consists  in  employing  boiling  sulphuric  acid  in  a  cast- 
iron  retort  with  molten  sulphur  floating  on  the  top.  In- 
stead of  sulphur,  carbon  has  been  used  with  91  %  acid ; 
in  this  case  carbon  dioxide  and  carbon  monoxide  are 
simultaneously  produced  (D.R.P.  196371/08).  In  B.P. 
1427/83  Ramsay  proposes  the  concentration  of  sulphur 
dioxide  by  absorption  from  the  weak  gases  with  sodium 
sulphite,  sodium  hydrogen  sulphite  being  produced,  which 
on  heating  gives  off  pure  sulphur  dioxide.  According  to 
Hart  (B.P.  13950/85)  sulphur  dioxide  is  produced  by  the 
action  of  sulphuric  acid  (S.G.  1*75)  on  finely  divided  iron 
sulphide  at  200°  C.  The  Hanisch  and  Schroder  process 
(patents  B.P.s  2621/83,  6404/85  and  6405/85 ;  D.R.P. 
36721/86  and  52025/90)  relates  to  the  absorption  of  sulphur 
dioxide  from  burner  gases  by  cold  water  and  subsequent 
expulsion  by  heat;  cf.  also  Basset,  B.P.  20667/13. 
Bergmann  and  Berliner  (D.R.P.  160940/02)  propose  to  realize 
the  same  objective  by  the  alternate  formation  of  Ca(HSO3)2 
and  Ca(H2PO4)2  by  the  action  of  sulphur  dioxide  on  CaHPO4 
and  subsequent  reversal  of  the  reaction  by  heating  to  100°  C. 
Moulin  and  Vandoni  (F.P.  432431/10)  prescribe  the  isolation 
of  sulphur  dioxide  by  compression  to  30  atms.  of  gases 
containing  10-12  %  of  sulphur  dioxide  followed  by  cooling  to 
o°  C.  by  means  of  the  cold  produced  by  the  expansion  of  the 
residual  gases  in  a  heat-interchanger.  Moore  and  Wolf,  in 
U.S. P.  1091689/14,  advocate  absorption  in  calcium  chloride 
solution  at  o°  C.  and  subsequent  release  by  evacuation. 
Similarly,  U.S.P.  1145579/15  of  Garner  and  Metals  Research 


SULPHUR  DIOXIDE  277 

Co.,  relates  to  the  sorptionof  the  gas  in  charcoal  and  B.P. 
107589/17  (Kaltenbach)  to  the  use  of  alcohol  for  the  same 
purpose. 

It  has  been  stated  above  that  the  only  process  in  use  on 
any  important  scale  for  the  manufacture  of  liquid  sulphur 
dioxide  is  the  Hanisch  and  Schroder  process,  which  uses 
dilute  burner  gases  as -a  source  of  sulphur  dioxide  ;  some 
account  will  therefore  be  given  of  the  possible  ways  of 
producing  such  gases  as  opposed  to  practically  pure  or 
highly  concentrated  sulphur  dioxide. 

Production  of  Dilute  Sulphur  Dioxide 

The  production  of  sulphur  dioxide  in  a  dilute  state  is 
undertaken  on  a  very  large  scale  in  connection  with  the 
manufacture  of  sulphuric  acid  and  sulphuric  anhydride  from 
iron  pyrites,  from  elementary  sulphur  or  from  zinc  blende, 
and  would  require  more  space  for  an  adequate  description 
than  can  be  allotted  in  the  present  volume.  Reference  should 
therefore  be  made  to  special  treatises  on  this  subject.  It 
will,  however,  be  desirable  to  mention  briefly  some  of  the 
more  important  patents  from  the  point  of  view  of  the  present 
problem. 

According  to  theory,  the  combustion  of  sulphur,  using 
the  minimum  quantity  of  air,  should  give  rise  to  a  gas 
containing  21  %  sulphur  dioxide,  but  even  when  elementary 
sulphur  is  used,  7-15  %  represents  the  values  realized  in 
practice.  If  less  air  is  used  there  is  a  tendency  for  the 
sulphur  to  sublime  as  such.  With  pyrites  the  concentration 
is  smaller. 

Dilute  sulphur  dioxide  may  be  produced  in  a  variety  of 
ways,  e.g.  by  melting  zinc  blende  with  zinc  sulphate  (Pernell, 
D.R.P.  1351/77)  ;  by  the  combustion  of  sulphuretted  hydro- 
gen (Pernell  and  Simpson,  B.P.  14711/86)  ;  by  roasting 
galena  with  calcium  carbonate  (Huntingdon  and  Eberlein, 
B.P.  8064/96)  ;  from  "  spent  oxide,"  and  as  a  by-product 
from  various  manufacturing  operations,  e.g.  cement  manu- 
facture (Basset,  B.P.  12027/12).  The  use  of  zinc  blende  is 
discussed  by  Hutin  (Moniteur  Scient.,  7,  (1917),  25)  ;  the 


278  INDUSTRIAL  GASES 

residue  is  more  valuable  than  in  the  case  of  iron  pyrites,  but 
the  operations  are  more  troublesome.  The  gases  from 
pyrites  burners  usually  contain  small  amounts  of  sulphur 
trioxide  formed  by  the  catalytic  action  of  the  burnt  pyrites. 
A  mixture  of  sulphur  dioxide  and  oxygen  was  formerly 
prepared  for  the  manufacture  of  sulphur  trioxide  by  dropping 
sulphuric  acid  into  incandescent  retorts. 

Concentration  of  Dilute  Sulphur  Dioxide 

The  Hanisch  and  Schroder  Process. — This  process  was 
first  taken  up  in  1885,  an  experimental  factory  being  erected 
by  Grillo  in  Germany,  making  12  cwt./diem  of  liquid  sulphur 
dioxide  from  gases  containing  6  %  sulphur  dioxide.  In 
1886,  a  plant  turning  out  6  tons/diem,  working  on  zinc  blende, 
was  operated  in  Silesia.  According  to  Molinari  a  factory 
should  have  a  minimum  output  of  8-10  tons/diem  for 
economical  working.  The  usual  method  of  operating  the 
process  is  as  follows  :  Gases  from  pyrites  burners  of  con- 
centration about  6  %  sulphur  dioxide  (not  below  4  %)  are 
passed  through  a  dust-retaining  chamber,  then  cooled 
thoroughly  and  passed  to  the  water  absorption  towers. 
Two  towers  packed  with  coke  and  plates  are  often  employed, 
arranged  in  series  with  counter-current  circulation  of  the 
water.  The  sulphur  dioxide  content  of  the  issuing  gases  is 
reduced  to  at  least  0*05  %,  while  the  water  leaving  the  first 
tower  contains  about  i  %  sulphur  dioxide.  In  order  to 
effect  the  removal  of  the  sulphur  dioxide  from  this  weak 
solution  with  the  greatest  economy  of  heat,  the  said  solution 
is  passed  first  through  a  leaden  heat-interchanger  in  counter- 
current  to  the  mixture  of  steam  and  sulphur  dioxide  leaving 
the  top  of  the  desaturation  tower.  leaving  this  inter- 
changer  at  a  temperature  of  about  85°  C.,  the  liquid  traverses 
a  coil  immersed  in  the  heated  liquid  in  the  sump  of  the 
desaturation  tower,  being  further  heated,  and  is  then  sprayed 
in  at  the  top  of  this  tower,  which,  according  to  D.R.P. 
52025/90,  contains  a  series  of  inclined  baffles,  steam  being 
injected  near  the  bottom.  The  liquid  flowing  out  is  practi- 
cally free  from  sulphur  dioxide  while  the  mixture  of  sulphur 


SULPHUR  DIOXIDE  279 

dioxide  and  steam  passes,  as  explained  above,  to  the  heat- 
interchanger  and  then  to  a  cooler,  the  condensed  water, 
containing  sulphur  dioxide,  from  both  being  returned  to 
the  middle  of  the  desaturation  tower. 

A  variation  is  described  in  D.R.P.  36721/86,  according 
to  which  the  mixture  of  sulphur  dioxide  and  steam  evolved 
on  boiling  the  dilute  liquor,  in  leaden  pans  heated  by  the 
burner  gases,  is  passed  up  a  tower  in  counter-current  to  a 
stream  of  cold  water.  The  excess  steam  serves  to  heat  the 
cold  water  practically  to  boiling  point ;  the  hot  water  passes  to 
a  heat-interchanger  in  counter-current  to  the  liquid  entering 
the  boiling-out  pans,  while  the  sulphur  dioxide  leaves  at  the  top, 
practically  dry.  In  both  cases,  final  drying  of  the  sulphur 
dioxide  is  effected  by  passage  up  a  coke  tower,  down  which  con- 
centrated sulphuric  acid  flows,  the  re-concentration  of  the  sul- 
phuric acid  being  accomplished  by  the  waste  heat  from  the 
py  ritesburners.  The  dry  sulphur  dioxide  then  passes  to  a  single- 
stage  bronze  pump,  where  it  is  compressed  to  2^-3  atms.  which 
suffices,  after  cooling,  to  produce  liquefaction  ;  an  oil-sealed 
gas-holder,  or  other  equilibrator,  is  employed.  The  liquid 
sulphur  dioxide  collects  in  a  large  wrought-iron  receiver  fitted 
with  a  relief  valve  for  the  nitrogen  and  oxygen  present,  which 
are  led  back  to  the  absorption  tower.  The  liquid  sulphur 
dioxide  produced  in  this  way  has  often  a  purity  of  99*8  %. 

The  preparation  of  aqueous  solutions  of  sulphur  dioxide 
demands  no  precautions  except  that  it  is  necessary  to  cool 
both  the  gas  and  the  water. 

Transport  of  Liquid  Sulphur  Dioxide. — Sulphur  di- 
oxide is  put  on  the  market  in  glass  "  siphons  "  for  laboratory 
use  in  steel  cylinders  holding  from  12  oz.  to  2  cwt.,  or,  in 
Germany,  in  tank  waggons  holding  as  much  as  10  tons  of 
sulphur  dioxide,  some  such  waggons  having  3  cylinders  about 
23  ft.  long  and  2  ft.  3  in.  diameter.  Cylinders  are  fitted 
with  bent  tubes  connected  to  the  inlet  valves  to  deliver 
either  liquid  or  gas  according  to  the  position  of  the  cylinder. 
These  tubes  also  serve  to  indicate  the  correct  degree  of 
filling  of  the  cylinder  ;  when  the  cylinder  is  erect  and  the 
valve  opened,  no  liquid  should  be  ejected. 


280  INDUSTRIAL  GASES 

According  to  German  regulations,  the  cylinders  are 
tested  to  30  atmospheres  and  the  maximum  degree  of  rilling 
is  i  kilo,  per  O'8  litres,  i.e.  78  lbs./ft.3,  or  according  to  Italian 
regulations,  i  kilo,  per  litre,  i.e.  62-5  lbs./ft.3  In  this  country 
no  specific  regulations  appear  to  exist,  but  the  practice  of  a 
prominent  firm  manufacturing  sulphur  dioxide  is  to  adopt 
a  maximum  filling  of  about  70  Ibs.  sulphur  dioxide  per  ft.3, 
the  cylinders  being  annealed  and  re-tested  (to  30  atms.)  at 
least  once  a  year. 

Applications  of  Sulphur  Dioxide 

The  various  applications  of  sulphur  dioxide  may,  for  the 
sake  of  convenience,  be  discussed  under  the  following 
headings  : — 

(1)  Manufacture  of  Sulphuric  Acid,  Sulphuric  Anhy- 
dride and  Sodium  Sulphate. — It  is  unnecessary  here  to  do 
more  than  mention  the  use,  on  an  enormous  scale,  of  sulphur 
dioxide  in  the  manufacture  of  sulphuric  acid  by  the  chamber 
process  and  of  sulphur  trioxide  by  the  "  contact  process," 
a  mixture  of  sulphur  dioxide  and  air  being  passed  over 
heated  finely-divided  platinum   supported   on   magnesium 
sulphate  or  asbestos,  or  over  iron  oxide.     Sulphur  dioxide 
is  also  used  in  the  manufacture  of  salt  cake  (sodium  sulphate) 
by  the  Hargreaves  process,  which  depends  on  the  action  of 
a  mixture  of  sulphur  dioxide,   steam  and  air  on  sodium 
chloride  at  400-540°  C.,  sodium  sulphate  and  hydrochloric 
acid  resulting. 

(2)  Manufacture  of  Wood  Pulp. — Sulphur  dioxide  is 
largely  used  in   the  preparation  of  wood  pulp  for  paper 
manufacture,    by    the    bisulphite    process;   liquid    sulphur 
dioxide  was  formerly  used  to  a  great  extent  in  the  prepara- 
tion of  the  liquor  and  for  bringing  up  to  strength,  but  now 
pyrites  gases  are  mostly  used. 

The  process  consists  in  boiling  fir  or  pine  in  small  pieces 
with  calcium  bisulphite  solution  containing  excess  sulphur 
dioxide  under  a  pressure  of  50-80  Ibs. /in.2  until  all  the 
incrusting  matter  is  dissolved,  and  then  mechanically 
separating  the  cellulose  from  the  residue  by  washing  and 


SULPHUR  DIOXIDE  281 

beating.  The  spent  lyes  contain  sugars  which  may  be 
fermented  with  the  production  of  alcohol,  it  being  stated 
that  some  4000  tons  of  alcohol  are  produced  annually  in 
Sweden  in  this  way.  After  the  bleaching  of  the  pulp,  sulphur 
dioxide  is  again  used  for  the  removal  of  the  last  traces  of 
chlorine.  It  is  important  that  the  sulphur  dioxide  used  should 
be  quite  free  from  sulphur  trioxide  and  some  manufacturers 
use  brimstone  in  preference  to  pyrites  on  this  account ;  the 
former  procedure  has  the  further  advantage  of  furnishing  a 
stronger  gas.  To  free  from  sulphur  trioxide  it  is  necessary 
to  wash  the  gases  with  water. 

In  the  manufacture  of  bisulphite  the  well-cooled  burner 
gases  are  brought  into  contact  with  lime  or  magnesium  lime. 
Various  systems  are  used  for  effecting  this  operation 
(cf.  Williams,  /.  Soc.  Chem.  Ind.,  (1913),  457) — (i)  the 
gases  are  injected  at  the  bottom  of  vessels  through  which 
a  slow  stream  of  milk  of  lime  flows ;  (2)  the  milk  of  lime  is 
fed  into  the  upper  of  two  closed  tanks  fitted  with  stirring 
gear,  while  the  sulphur  dioxide  gases  are  led  into  the  lower 
tank  and  flow  to  the  upper  one,  being  assisted  by  the  reduced 
pressure  produced  by  a  pump  attached  to  the  latter — when 
the  lower  tank  is  saturated  with  sulphur  dioxide  its  charge 
of  liquid  is  run  off  and  replaced  by  that  from  the  upper  one 
which  is  filled  up  with  fresh  milk  of  lime;  and  (3)  one  or  more 
towers  constructed,  e.g.  of  reinforced  concrete,  and  from  60- 
100  ft.  high,  are  filled  with  limestone  and  water  is  sprayed 
in  at  the  top  while  the  sulphur  dioxide  gases  are  admitted 
at  the  bottom — if  two  towers  are  used,  counter-current 
working  is  adopted.  The  third  system  has  the  advantage  of 
using  unburnt  limestone  and  of  requiring  less  pressure  to 
effect  the  passage  of  the  gases. 

In  each  case  the  liquor  passes  to  storage  tanks  and  is 
enriched  by  the  gases  evolved  in  the  digestion  of  the  wood. 
The  following  is  a  typical  example  of  the  percentage  com- 
position of  such  a  liquor  : — 

Calcium  oxide        0-98 

Free  sulphur  dioxide        2-65 

Combined  sulphur  dioxide          . .         . .     1-15 


282  INDUSTRIAL  GASES 

(3)  In  Refrigeration  Plant. — Sulphur  dioxide  is  used  to 
a  considerable  extent  in  refrigeration  plant,  although,   of 
course,  it  is  much  less  convenient  for  general  purposes  than 
the   commonly  employed   ammonia.     The   use   of  sulphur 
dioxide  for  this  purpose  was  originally  developed  by  Pictet, 
its  chief  advantages  over  other  substances,  such  as  ammonia, 
lie  in  its  non-injurious  action  on  food,  etc.,  if  escape  should 
occur,   its  low   working  pressure   and   its   applicability   to 
conditions  where  no  cooling  water  is  available.     On  the 
other  hand,  a  considerably  larger  compressor  capacity  is 
required   than   is   the   case   with   ammonia,  for   example  ; 
sulphur  dioxide  plants  are  only  used  for  relatively  small 
installations.     Reference  has  already  been  made  to  the  action 
on  iron   of  moist  sulphur  dioxide   when  warm ;    in  this 
connection  it  is  important  to  avoid,  as  far  as  possible,  the 
presence  of  air  in  sulphur  dioxide  systems  as  formation  of 
sulphuric  acid  may  occur  and  set  up  corrosion.     Although 
iron  is  protected  to  some  extent  by  an  insoluble  coating, 
bronze  is  often  used  for  the  compressors.     Sulphur  dioxide 
has  some  lubricating  properties  and  consequently  the  use 
of  oil  is  unnecessary. 

(4)  As  a  Solvent. — In  spite  of  the  relative  difficulty  of 
handling  a  liquid  with  a  high  vapour  pressure  at  ordinary 
temperatures,    for   such  purposes,    liquid   sulphur   dioxide 
is  used  in  certain  extraction  operations,  the  principal  appli- 
cation being  in  the  extraction  of  bones  in  the  manufacture 
of  glue.     In  the  extraction  of  the  fat,  sulphur  dioxide  has 
the  advantage  over  other  solvents  of  greater  penetration  of 
the  animal  membranes.     After  this  operation  is  completed, 
calcium   phosphate   is   extracted   by    an    aqueous   sulphur 
dioxide  solution.     Sulphur  dioxide  has  been  proposed  as  a 
substitute  for  the  inflammable  carbon  disulphide  or  benzol 
in  oil  extraction,  but  no  important  technical  progress  appears 
to  have  been  made  in  this  direction. 

(5)  For  Bleaching  Purposes. — Sulphur  dioxide  is  used 
to  a  considerable  extent  as  a  bleaching  agent  for  delicate 
fabrics,  etc.,  which  would  be  injured  by  the  action  of  more 
drastic  agents,  such  as  chlorine.     The  bleaching  action  of 


SULPHUR  DIOXIDE  283 

sulphur  dioxide,  unlike  that  of  most  other  agents/  depends 
not  on  oxidation  but  on  reduction,  resulting  in  the  formation 
of  colourless  leuco-compounds,  and  in  being  reversible, 
e.g.  by  the  action  of  light.  The  gas  is  more  effective  than  the 
solution,  but  its  action  is  favoured  by  damping. 

Among  substances  bleached  by  sulphur  dioxide  may  be 
mentioned  wool,  silk,  straw,  cereals  (action  injurious), 
oils  and  their  fatty  acids  (cf .  Hird  and  L,loyd,  /.  Soc. 
Chem.  Ind.,  (1912),  317). 

(6)  As   a   Disinfectant.— Sulphur   dioxide  has  strong 
germicidal  properties  and  is  used  for  the  disinfection  of 
rooms  (by  combustion  of  sulphur  or,  more  conveniently,  in 
the  form  of  liquid),  in  beer  and  wine  manufacture,  for  the 
preservation  of   fruit,  meat,  syrups,  etc.,  in  ships  for  rapid 
disinfection  and  for  the  destruction  of  rats. 

It  is  also  used  for  the  interruption  of  fermentation  in  wine, 
etc.,  and  in  the  treatment  of  cutaneous  diseases. 

(7)  Other  Applications. — Among  other  applications  of 
sulphur  dioxide  may  be  cited  its  use  as  an  "  antichlor," 
already  referred  to  in  the  case  of  wood  pulp,  i.e.  the  removal 
of  the  last  traces  of  chlorine  from  bleached  material ;    the 
refining  of  crude  petroleum ;  the  softening  of  hides  in  tanning  ; 
the  extraction  of  alum  from  shale,  and  in  sugar  manufacture, 
where  sulphur  dioxide  is  passed  through  the  juices  after, 
and  sometimes  before,  their  treatment  with  lime  which  is 
converted  into  the  difficultly  soluble  calcium  sulphite,  the 
juice  being  bleached  at  the  same  time.     Sulphur  dioxide 
has  only  a  slight  inverting  action  on  sucrose.     In  admixture 
with  carbon  dioxide,  sulphur  dioxide  is  used  for  fire  ex- 
tinction, in  the  manufacture  of  tartaric  acid,  etc.     The  use 
of  sulphur  dioxide  has  been  proposed  for  improving  the 
efficiency  of  engines  by  utilizing  the  heat  of  the  exhaust 
steam. 

The  Estimation  and  Testing  of  Sulphur  Dioxide.— 
Sulphur  dioxide  is  readily  detected  by  its  characteristic  odour 
or  by  its  reducing  action  on  potassium  dichr ornate  paper, 
etc.,  and  may  be  conveniently  estimated  by  titration  with 
standard  iodine  solution. 


284  INDUSTRIAL  GASES 

According  to  Haller  (/.  Soc.  Chem.  Ind.,  (1919),  52  T) 
dilute  sulphur  dioxide  is  best  estimated  by  absorbing  in 
caustic  soda  solution,  and,  after  acidifying  strongly  with 
hydrochloric  acid,  titrating  with  potassium  iodate.  Sponta- 
neous oxidation  of  the  sodium  sulphite  to  sulphate  is  pre- 
vented by  the  addition  of  a  negative  catalyst,  e.g.  glycerol, 
to  the  caustic  soda  solution.  On  titration  of  an  aqueous 
solution  of  sulphur  dioxide  with  a  strong  alkali,  such  as 
caustic  soda,  methyl  orange  gives  the  point  of  conversion 
of  the  caustic  soda  into  sodium  hydrogen  sulphite. 

liquid  sulphur  dioxide  is  tested  for  water  by  with- 
drawing a  sample  of  the  liquid  under  pressure  and  evapora- 
ting through  tared  calcium  chloride  tubes.  Sulphuric  acid 
and  lubricating  oil  are  determined  in  the  residue.  Arsenic 
also  may  be  looked  for  when  the  sulphur  dioxide  is  to  be 
used  in  connection  with  food-stuffs.  Carbon  dioxide  and 
air  may  be  estimated  by  bubbling  a  considerable  quantity 
of  the  gas  through  chromic  acid  solution  and  examining  any 
gas  passing  through  (cf.  lounge,  "Technical  Gas  Analysis," 
1914,  p.  361). 

REFERENCES   TO  SECTION   X. 

Teichmann,  "  Komprimierte  und  verfliissigte  Case."     Halle,  1908. 
Lunge,  "  Sulphuric  Acid  and  Alkali,"  vol.  i.     Ixmdon,  Fourth  Edition, 


Harpf,  "  Flussiges  Schwefeldioxyd,  Darstellung,  Eigenschaften  und 
Versendung  desselben,"  Sammlung  chem.  und  chem-techn.  Vortrage  von 
Ahrens,  Bd.  v.,  1900. 


SECTION  XI.— NITROUS  OXIDE 

Properties  of  Nitrous  Oxide. — Nitrous  oxide  is  a  colour- 
less gas  with  a  faint  but  characteristic  odour  resembling 
that  of  burnt  sugar.  It  is  readily  soluble  in  cold  water  as 
below  : — 


Temperature  °C  

5 

15 

25 

C.c.  of  gas  (measured  at  N.T.P.)  dissolved  by  i 

c.c.    of    water  under  a  pressure  of    i   atm., 

exclusive  of  water  vapour 

1-0480 

0-7378 

o'5443 

The  gas  is  found  on  the  market  in  the  form  of  liquid, 
the  vapour  pressure  varying  with  temperature  as  follows  : — 


Temperature  CC. 
Vapour  pressure  in  atms. 

/Regnault  (1862) 
\Villard  (1897) 

o 
36T 
30-8 

10 

44-8 

20 

55*3 
49'  4 

30 
68-0 

40 
83'4 

Liquid  nitrous  oxide  is  very  mobile  and  is  colourless. 
The  other  important  physical  properties  will  be  found  in 
Tables  12  and  13,  on  pp.  53-56. 

Nitrous  oxide  is  an  endothermic  compound — 

2N2  +  O2  =  2N2O  —  38,000  calories. 

It  is,  consequently,  in  a  metastable  condition  at  the 
ordinary  temperature.  According  to  Hunter  (Z.  physik. 
Chem.,  53,  (1905),  441)  nitrous  oxide  is  decomposed  at  700- 
900°  C.  into  its  elements  with  the  formation  of  small  quanti- 
ties of  higher  oxides,  especially  at  the  higher  temperatures  ; 
moisture  was  found  to  have  little  influence.  A  rough 
calculation  of  the  equilibrium  constant,  according  to  the 
Nernst  Heat  Theorem,  for  a  temperature  of  2000°  C. — 


38,000 


286  INDUSTRIAL  GASES 

indicates  that  at  atmospheric  pressure  the  equilibrium 
condition  corresponds  to  0*00013  %  °f  nitrous  oxide.  Even 
under  the  more  favourable  conditions  of  a  pressure  of  1000 
atmospheres  and  the  same  temperature  the  equilibrium  per- 
centage is  only  raised  to  about  0*004  %• 

It  was  observed  by  Wroczynski  (1910)  chat  no  decom- 
position occurred  at  420°  C.  under  a  pressure  of  600  atmo- 
spheres. 

Nitrous  oxide  is  an  energetic  supporter  of  combustion 
of  e.g.  carbon  or  sulphur,  provided  that  a  sufficiently  high 
temperature  for  the  initiation  be  first  produced.  It  forms 
an  explosive  mixture  with  hydrogen  while  a  mixture  with 
carbon  disulphide  burns  with  a  very  actinic  blue  flame. 
Its  use  as  an  anaesthetic  was  first  suggested  by  Humphrey 
Davy  in  1800  ;  in  small  amount  it  produces  a  kind  of 
intoxication,  hence  the  name  "  laughing  gas." 

Manufacture 

From  Ammonium  Nitrate. — Nitrous  oxide  may  be 
produced  from  other  nitrogen  compounds  in  a  variety  of 
ways,  e.g.  by  the  reduction  of  nitric  acid  with  a  mixture  of 
hydrochloric  acid  and  stannous  chloride  (Campari)  and  by 
the  reduction  of  nitrites  with  sulphur  dioxide,  sodium 
amalgam,  etc.,  but  the  only  method  of  any  practical  im- 
portance is  that  depending  on  the  decomposition  of  ammonium 
nitrate  by  heating — 

NH4NO3  =  N2O  +  2H2O  +  25,000  calories. 

The  decomposition  begins  at  170°  C.  and  is  fairly 
energetic  at  215°  C.  It  is  important  that  the  ammonium 
nitrate  should  be  pure,  especially  as  regards  chlorine  com- 
pounds, and  great  care  must  be  taken  not  to  overheat  as  the 
decomposition  may  become  explosively  violent. 

A  description  is  given  by  Flagg  ("  Art  of  Anaesthesia/' 
1916)  of  a  plant  at  the  Lakeside  Hospital,  Cleveland. 
Ammonium  nitrate,  in  charges  of  40  Ibs.,  is  heated  in  one  of 
two  aluminium  retorts  to  200°  C.  and  the  resulting  gases 
passed  through  a  cooling  coil  to  a  wash  bottle  containing 


NITROUS   OXIDE  287 

potassium  permanganate  solution  in  order  to  remove  higher 
oxides  of  nitrogen.  The  nitrous  oxide  is  then  washed  with 
caustic  soda  in  a  tower  packed  with  coke  to  remove  nitric  acid, 
freed  from  alkali  by  passing  through  sulphuric  acid  and 
finally  washed  with  water.  The  gas  passes  into  a  holder 
and  is  subsequently  either  compressed  to  about  100  atmo- 
spheres and  liquefied  or  stored  as  gas  at  a  pressure  of  about 
100  lbs./in.2  in  pressure  vessels  from  which  it  is  distributed 
at  a  pressure  of  5  lbs./in.2  through  meters  to  the  operating 
rooms.  The  theoretical  yield  of  nitrous  oxide  is  about 
4* 7  ft.3/lb.  ammonium  nitrate,  whereas  about  4  ft.3  are 
obtained  in  practice.  On  this  basis  1000  ft.3  require  about 
250  Ibs.  of  ammonium  nitrate.  Instead  of  aluminium,  cast 
iron  may  be  used  as  the  retort  material. 

According  to  L,idoff,  a  mixture  of  2  parts  of  ammonium 
nitrate,  previously  dried  at  105°  C.,  with  3  parts  of  sand  is 
heated  to  260-285°  C.,  the  resulting  gas  being  washed  first 
with  a  solution  of  sodium  sulphide  or  a  suspension  of  iron 
sulphide  and  then  with  an  emulsion  of  ferrous  sulphate  in 
concentrated  sulphuric  acid,  to  remove  nitric  oxide.  The 
expensive  ammonium  nitrate  may  be  replaced  by  a  mixture 
of  ammonium  sulphate  and  sodium  nitrate  (Smith  and 
Blmore,  B.P.  9023/91).  Specified  proportions  of  the  two 
salts  are  mixed  and  heated  to  not  higher  than  230°  C.  at  the 
beginning  of  the  operation,  the  temperature  rising  to  about 
300°  C.  at  the  end.  B.P.  11828/13,  of  Torley  and  Matter, 
prescribes  the  continuous  injection  of  ammonium  nitrate 
either  in  solution  or  as  solid  in  convenient  form,  into  a  heated 
reaction  vessel  containing  sand,  shot,  molten  metal,  etc., 
and  fitted  with  a  stirrer. 

By  Other  Methods. — In  B.P.  1 9074/00 Marston  describes 
the  preparation  of  mixtures  of  nitrous  oxide  and  nitrogen 
by  passing  regulated  proportions  of  ammonia  and  air  freed 
from  carbon  dioxide  over  heated  copper.  The  use  of  this 
method  for  the  preparation  of  nitrogen  has  been  already 
described,  p.  113.  Higher  oxides  of  nitrogen  are  removed 
by  passing  through  iron  shavings,  followed  by  ferrous 
sulphate  solution  and  then  alkali. 


288  INDUSTRIAL  GASES 

By  rapidly  cooling,  at  the  point  of  maximum  nitrous 
oxide  content,  a  nitrogen- oxygen  flame  produced  by  com- 
bustion (not  of  hydrogen)  or  by  electrical  means,  Sodermann, 
in  F.P.  411785/10,  claims  the  production  of  nitrous  oxide, 
which  is  separated  from  nitrogen  by  liquefaction  after 
removal  of  the  carbon  dioxide.  On  similar  lines  is  F.P. 
415594/10  of  Pictet,  according  to  whom  a  mixture  of  55 
volumes  of  oxygen  with  45  volumes  of  nitrogen  is  forced 
centrally  into  a  vessel  through  an  oxy-acetylene  flame 
issuing  from  a  flattened  annulus.  A  particular  part  of  the 
flame  is  cooled  by  jets  of  water  which  absorbs  the  nitrous 
oxide.  A  yield  of  25  %  of  nitrous  oxide  is  claimed. 

Purification 

As  indicated  above,  nitrous  oxide  is  best  freed  from 
nitric  oxide  by  scrubbing  with  ferrous  sulphate  solution, 
while  chlorine,  which  may  be  derived  from  ammonium 
chloride  present  in  the  ammonium  nitrate  used  in  its  pre- 
paration, can  be  removed  by  caustic  soda  solution  or  other 
suitable  means.  Ammonia  may  be  removed  by  washing 
with  sulphuric  acid.  According  to  Villard,  further  purifi- 
cation may  be  effected  by  fractional  distillation  of  liquid 
nitrous  oxide,  any  nitrogen  going  off  in  the  first  fraction,  or 
by  the  formation  of  a  hydrate  (below  o°  C.)  and  subsequent 
decomposition  by  heating. 

Applications  of  Nitrous  Oxide 

The  chief  use  of  nitrous  oxide  is  as  an  anaesthetic, 
especially  for  dental  operations.  The  practical  application 
of  the  anaesthetic  property  of  nitrous  oxide  is  due  to  Colton 
and  Wells  in  1844.  It  is  now  administered  almost  exclu- 
sively in  conjunction  with  oxygen  since  with  nitrous  oxide 
alone  it  is  difficult  to  produce  sufficiently  lasting  anaesthesia 
without  danger  of  asphyxia.  The  proportion  of  oxygen 
used  is  from  5-25  %  ;  usually  about  10  %  at  the  beginning 
with  subsequent  increase  according  to  the  susceptibility 
of  the  patient.  The  effect  is  very  evanescent  in  any  case, 


NITROUS   OXIDE  289 

generally  lasting  about  40  seconds.  On  the  average  the 
time  for  the  production  of  anaesthesia  is  a  little  less  than  one 
minute  and  about  one  ft.3  of  nitrous  oxide  is  required. 
Among  anaesthetics  it  is  the  one  most  free  from  constitutional 
disturbances,  but  is  only  suitable  for  cases  in,  which  complete 
muscular  relaxation  is  not  essential. 

Nitrous  oxide  is  obtained  in  steel  cylinders  containing 
from  about  6  oz.  to  about  50  Ibs.  of  the  liquid,  i.e.  from  3-2- 
430  ft.3  of  the  gas.  One  Ib.  of  the  liquid  is  equivalent  to 
about  8-55  ft.3  of  gas  at  15°  C.  For  purposes  of  anaesthesia 
it  is  important  that  the  nitrous  oxide  should  be  free  from 
chlorine,  other  oxides  of  nitrogen,  combined  organic  matter, 
solids,  liquids,  etc.,  and  should  contain  at  least  95  %  nitrous 
oxide. 

A  representative  sample  of  the  commercial  product 
appears  to  have  a  percentage  composition  somewhat  as 
follows  (Baskerville  and  Stephenson,  J.  Ind.  Eng.  Chem.,  3, 
(1911),  579)  :- 

Nitrous  oxide 96-99 

Water 0*15 

Carbon  dioxide traces 

Ammonia  O'0oi-o-oo6 

Oxygen . .  traces 

Nitrogen  . .          . .          . .          . .  O'i6~3'94 

According  to  the  same  authors  the  presence  of  chlorine 
and  of  the  higher  oxides  of  nitrogen  may  be  detected  by 
passing  some  10  litres  of  the  gas  through  solutions  of  silver 
nitrate  and  ferrous  sulphate.  The  nitrous  oxide  may  be 
estimated  by  passing  the  dry  gas  together  with  hydrogen 
over  heated  reduced  copper  with  subsequent  reduction  of 
any  copper  oxide  by  hydrogen,  the  water  produced  being 
determined  in  the  usual  way.  In  view  of  the  fact  that 
nitrous  oxide  is  an  endothermic  compound,  the  stability 
of  the  liquid  has  been  the  subject  of  some  enquiry  (liquid 
acetylene  or  even  the  compressed  gas  is,  of  course,  a  highly 
dangerous  substance  owing  to  its  endothermic  character). 

A  propos  of  the  unexplained  explosion  of  a  cylinder  of 
A.  IQ 


290  INDUSTRIAL  GASES 

liquid  nitrous  oxide,  Rasch  (Z.  fiir  komp.  u.  fliissige  Case, 
(1904),  159)  examined  the  question  as  follows.  By  heating 
platinum  or  iron  wires  in  the  liquid,  only  local  decomposition 
was  observed  as  a  rule  when  the  temperature  of  the  liquid 
was  below  30°  C.,  but  occasionally  explosion  occurred,  even 
with  the  temperature  of  the  liquid  as  low  as  o°  C.  in  one 
instance.  Above  30°  C.  the  decomposition  propagated 
itself  throughout  the  mass.  Electric  sparks  produced  no 
explosion  even  at  80°  C.  Generally  speaking,  detonation 
only  occurred  with  an  energetic  temperature  rise  above  the 
critical  temperature  of  the  liquid,  viz.  38-8°  C. ;  direct 
heating  of  the  cylinder  produced  no  detonation,  although 
the  cylinder  burst  owing  to  the  high  pressure  generated. 

The  possibility  of  the  production  of  sparks  from  the 
presence  of  suspended  solid  matter  is,  however,  preferably 
minimized  by  always  opening  the  valve  with  the  cylinder  in 
a  vertical  position,  thus  avoiding  the  passage  of  solid  particles 
through  the  valve.  Further,  just  as  in  the  case  of  oxygen,  oil 
should  be  scrupulously  excluded  from  the  valves  and  con- 
nections. As  in  the  case  of  other  liquid  gases,  special  care 
must  be  taken  with  regard  to  the  degree  of  filling  of  cylinders 
owing  to  the  rapid  increase  in  volume  of  the  liquid  with 
temperature.  Reference  to  p.  45  will  indicate  the  permissible 
content  of  a  given  vessel. 


SECTION  XII.— ASPHYXIATING   GASES 

Introduction. — During  the  war  the  manufacture  and 
use  of  asphyxiating  gases  attained  such  proportions  that 
a  book  dealing  with  industrial  gases  would  be  incomplete 
without  a  brief  reference  to  this  branch  of  the  subject. 

Although  one  hopes  that  the  production  of  the  various 
gases  will  never  be  revived  for  like  purposes,  there  is  no 
doubt  that  the  knowledge  gained  as  regards  the  technical 
preparation  and  properties  of  many  substances  previously 
unknown  except  to  the  few  will  prove  to  be  of  signal  service 
in  the  industries,  particularly  in  the  realm  of  organic  chemistry. 
Further,  a  number  of  the  substances  may  be  found  useful 
for  such  purposes  as  the  extirpation  of  various  pests  harmful 
to  vegetation. 

Since  most  of  the  gases,  such  as  chlorine,  come  under 
subjects  treated  in  other  volumes  of  this  series,  their  prepara- 
tion cannot  be  dealt  with  in  any  detail ;  also,  in  most  cases, 
the  published  information  in  this  connection  is  very  meagre 
at  present. 

The  Development  of  Gas  Warfare.-— The  initiation  of 
gas  warfare  was  made  by  the  Germans  in  April,  1915,  con- 
sisting in  the  use  of  chlorine  discharged  from  cylinders  of 
the  liquid,  disposed  at  regular  intervals  along  the  front  line, 
with  far-reaching  effects  on  our  unprotected  troops.  Emer- 
gency respirators  were  rapidly  improvised  and  the  subsequent 
development  was  determined  by  counter-efforts  of  a 
defensive  and  offensive  character  respectively. 

For  a  proper  understanding  of  the  subject  it  will  be 
necessary  briefly  to  consider  the  factors  determining  the 
success  or  otherwise  of  the  operations.  One  of  the  most 
important  points  is  the  maintenance  of  a  high  concentration 
— from  this  standpoint  0*1  %  is  a  fairly  high  concentration 


292  INDUSTRIAL  GASES 

while  0*01  %  is  quite  effective  with  most  gases,  e.g.  phosgene 
— and  this  is  dependent  chiefly  on  the  wind,  the  velocity  of 
which  should  be  between  the  limits  of  say,  4  and  12  miles  per 
hour,  and  also  to  some  extent  on  the  slope  of  the  country.  In 
order  to  ensure  the  safety  of  the  attacking  troops,  especially 
as  the  line  may  often  be  very  irregular,  the  wind  should 
approach  normality  to  the  general  direction  of  the  line. 
According  to  Auld  (J.  Wash.  Acad.  Sci.,  8,  (1918),  45), 
the  deviation  tolerated  by  the  Germans  was  about  40° 
on  either  side  of  the  normal.  The  density  of  the  gas  is 
not  so  important  as  is  sometimes  imagined,  since  dilution 
to  a  concentration  of  the  order  of  cri  %  occurs  very 
rapidly  and  the  density  of  such  a  mixture  does  not  differ 
appreciably  from  that  of  normal  air  whatever  the  density 
of  the  gas. 

Perhaps  the  most  important  matters  from  a  practical 
point  of  view  are  (i)  the  toxicity  ;  (2)  the  difficulty  of 
providing  protection  against  the  gas  ;  (3)  the  ease  of  manu- 
facture hi  the  large  quantities  required;  and  (4)  the  con- 
venience of  transport.  Condition  (4)  points  to  the  advantage 
of  non-permanent  gases,  since  a  given  cylinder  filled  with 
liquid  contains  a  considerable  weight  of  poison  at  a  relatively 
low  pressure  ;  chlorine,  although  suitable  as  regards  (i),  (3) 
and  (4),  was  soon  found  wanting  as  regards  (2),  being  very 
reactive  and  easily  absorbed  by  alkalis,  thiosulphate,  etc. 
The  most  important  gas  for  this  type  of  attack  has  been 
phosgene  (COC12)  (cf.  p.  252),  which  while  possessing  the 
other  desiderata  has  also  the  advantage  of  being  only  slowly 
hydrolysed  by  alkalis.  Phosgene  is  much  less  irritating 
than  chlorine  but  has  an  insidious  delayed  physiological 
action.  However,  absorbents  were  soon  found  in  sodium 
phenate  and  especially  in  urotropine — hexamethylenete- 
tramine — which  two  substances  in  conjunction  gave  pro- 
tection against  concentrations  of  O'l  %  when  used  in  the 
impregnated  flannel  type  of  respirator,  a  valve  being 
provided  for  exhalation.  This  type  of  respirator  was  soon 
entirely  susperseded  by  the  box  type,  which  consisted  of  a 
chamber  filled  with  granules  of  specially  activated  charcoal 


ASPHYXIATING  GASES  293 

possessing  the  property  of  absorbing  gases,  especially  those 
of  high  critical  temperature  in  which  category  practically  all 
the  poison  gases  are  to  be  found.  The  box  is  connected  to 
the  mouth  by  means  of  a  flexible  corrugated  rubber  tube 
ending  in  a  mouthpiece  and  nosepiece,  suitable  inspiration 
and  expiration  valves  being  fitted.  This  type  of  respirator 
has  the  advantage  of  simplicity  combined  with  effective 
protection  for  long  duration  attacks  for  practically  all  the 
gases  used,  and  is  very  easily  recharged.  For  short  periods 
concentrations  of  several  percents  can  be  dealt  with.  Much 
depends  on  the  previous  history  of  the  charcoal,  particularly 
as  regards  heat  treatment,  also  on  the  wood  from  which 
it  has  been  made.  The  enclosed  oxygen  breathing  apparatus, 
while  affording  an  absolute  protection,  has  only  a  short  time 
of  action  and  is  much  too  heavy  and  cumbersome. 

Further  attempts  to  use  cylinders  were  made  in  the 
direction  of  increasing  the  concentration,  but  the  cumber- 
some and  vulnerable  nature  of  the  equipment,  which  was  an 
unwelcome  addition  to  the  front  line  trenches,  the  need  for 
a  special  corps  of  operators,  the  noise  produced  by  the 
discharge  and  the  danger  of  part  of  the  attacking  line  being 
gassed,  led  to  their  almost  complete  supersedence  by  poison- 
charged  projectiles.  The  shells  could  be  placed  with  accuracy 
where  required  and  their  use  made  the  operations  independent 
of  the  wind.  Gas  attacks  by  shells  are  best  made  with 
concentration  over  a  relatively  small  area.  Hand  grenades 
have  also  been  used  to  some  extent.  In  addition  to  sub- 
stances which  are  primarily  poisonous,  considerable  use 
has  been  made  of  "  lachrymators,"  i.e.  substances  which 
attack  the  eyes,  producing  weeping,  and  also  the  mucous 
membranes,  e.g.  benzyl  bromide,  xylyl  bromide,  chloropicrin 
(CC13  .  NO2),  phenylcarbylamine  chloride  (C6H6  .  N  :  CC12). 
With  some  lachrymatories  a  concentration  of  O'oooi  %  is 
sufficient  to  affect  the  eyes  seriously.  Similar  irritants, 
which  are  not  highly  developed  lachrymators,  may  also  be 
used,  the  best  known  member  of  this  class  being  the  deadly 
"  mustard  gas,"  j8£'-dichloroethyl  sulphide  (CH2C1 .  CH2  . 
S  .  CH2  .  CH2C1) .  This  substance,  even  in  the  state  of  vapour, 


294  INDUSTRIAL  GASES 

has  a  most  extraordinary,  inflammatory  action  on  the  skin, 
the  more  insidious  because  not  immediate,  while  its  after- 
effects on  the  eyes  and  mucous  membranes  are  most  serious, 
blindness  often  resulting. 

Among  other  substances  may  be  mentioned  trichloro- 
methyl-chloroformate  (Cl .  CO .  O .  CC13)  which  is  poisonous  but 
not  lachrymatory,  and  diphenyl-chloroarsine  (As(C6H5)2Cl) 
which,  when  suspended  in  the  air,  causes  very  violent 
sneezing  in  addition  to  its  lachrymatory  and  very  toxic  action. 
The  lachrymatory  and  irritant  substances  just  referred  to, 
being  in  most  cases  liquid,  were  practically  always  used  in  shells 
or  hand  grenades ;  phosgene  was  also  used  in  shells.  Hydro- 
cyanic acid  was  apparently  not  employed  by  the  Germans, 
probably  on  account  of  its  temporary  action  if  the  dose  is 
insufficient  to  produce  death  at  once  and  of  its  easy  arrest- 
ment ;  nickel  salts  or  alkalis  may  be  used  as  absorbents. 

The  number  of  substances  which  have  been  employed  is 
very  large,  the  element  of  surprise  being  one  of  the  most 
important  tactical  points. 


PART  III.— GASEOUS   FUELS 

SECTION  XIII 

General  Considerations. — The  subject  of  gaseous  fuels  is 
one  which  is  receiving  great  attention  at  the  present  moment 
on  account  of  its  bearing  on  the  question  of  thermal  efficiency 
in  heating  processes  generally.  This  matter  is  of  great 
importance  in  connection  with  the  conservation  of  our 
fuel  resources,  and  particularly  at  the  present  time,  in  con- 
nection with  the  shortage  of  labour  and  the  restricted  supply 
of  oil  fuel  for  industrial  operations  owing  to  the  reduced 
tonnage  and,  during  the  war,  to  the  demands  of  the  Navy. 

The  principal  possibilities  for  increased  economy  are 
(i)  the  utilization  of  low  grade  coal  with  high  ash  content, 
and  other  fuel  which  would  otherwise  be  useless,  e.g.  peat, 
waste  wood,  straw  and  other  refuse  may  be  used  with  some 
types  of  producers  ;  (2)  the  greater  ease  of  effective  thermal 
regeneration  with  gaseous  fuels  and  the  avoidance  of  the 
large  excess  of  air  necessary  with  solid  fuel,  especially  when 
high  temperatures  are  required,  enable  better  thermal 
efficiency  to  be  obtained  in  spite  of  a  certain  minimum  loss 
of  energy  in  the  preliminary  gasification  of  the  solid  fuel ; 
(3)  the  recovery  of  the  greater  part,  about  70  %,  of  the 
nitrogen  present  in  the  coal,  as  ammonia,  a  valuable  national 
asset  both  for  war  purposes,  in  connection  with  explosives, 
and  also  for  use  as  a  fertilizer  ;  and  (4)  the  much  greater 
efficiency  of  the  gas  engine  as  a  source  of  power  in  comparison 
with  the  steam  engine,  at  any  rate  for  relatively  small  plants. 

Among  other  advantages  afforded  by  the  use  of  gaseous 
fuel,  are  the  much  greater  ease  of  control,  i.e.  the  adjustment 
of  temperature  or  of  the  reducing  or  oxidizing  nature  of  the 
atmosphere  of  a  furnace  ;  the  possibility  of  shutting  off  the 


296  INDUSTRIAL  GASES 

fuel  supply  immediately  when  finished  with ;  the  absence 
of  smoke  and  ash  ;  and  the  ease  of  distribution  from  a  central 
station. 

The  success  of  various  high  temperature  operations  of  the 
highest  importance  is  directly  attributable  to  the  introduction 
of  gaseous  fuels  of  low  calorific  value  but  cheap,  burnt  in 
regenerative  furnaces,  e.g.  in  the  open  hearth  furnace,  in 
the  heating  of  coal  gas  retorts,  etc. 


Fundamental  Principles  relating  to  the  Use  of 
Gaseous  Fuels 

In  Table  29  are  given  typical  examples  of  composi- 
tions, based  on  averages  of  the  analyses  given  by  a  number 
of  authorities,  of  the  various  gaseous  fuels,  together  with 
some  of  their  more  important  characteristics  with  which 
we  shall  deal  presently. 

Calorific  Value. — An  important  point  in  the  comparison 
of  gaseous  fuels  is  the  question  of  calorific  value. 

Reference  has  already  been  made  to  the  necessity  for 
discrimination  between  "  gross  "  and  "  net  "  calorific  values, 
and  although  the  latter  term  has  no  very  precise  significance 
(cf .  p.  13)  its  use  is  convenient  in  connection  with  most  opera- 
tions of  heating.  Observations  relating  to  British  and 
French  practice  have  been  made  on  p.  13  ;  in  the  United 
States  it  is  usual  to  use  the  gross  value  for  the  comparison 
of  fuels,  while  in  German  and  Austrian  practice  the  products 
of  combustion  are  assumed  to  be  cooled  to  100°  C.,  the  water 
remaining  as  steam. 

We  shall  see,  however,  that  the  value  of  a  gas  as  a  fuel 
cannot  be  expressed  in  terms  of  calorific  value  alone. 

The  Mechanism  of  Flame. — The  subject  of  the  pro- 
perties of  flames  is  an  extensive  one,  and  we  must  confine  our 
attention  here  to  a  few  of  the  more  practical  aspects  of  the 
question.  Usually  the  most  important  characteristic  of  a  flame 
in  relation  to  furnace  work  is  its  temperature.  The  temper- 
atures of  particular  portions  of  a  flame  are  best  determined 
by  using  several  thermocouples  of  different  diameter  wires, 


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298  INDUSTRIAL  GASES 

plotting  the  results  and    extrapolating  for  zero  thickness 
of  wire. 

Turning  to  factors  determining  flame  temperatures,  it 
is  obvious  that,  assuming  the  combustion  to  be  adiabatic, 
the  flame  temperature  will  be  represented  by  the  following 
fraction,  sometimes  termed  the  calorific  intensity  : — 

Heat  of  combustion  of  the  components  of  the  mixture 


Mean  thermal  capacity  of  the  products  per  degree  C.  over 
the  temperature  range  in  question 

neglecting  any  dissociation  at  the  flame  temperature.  Even 
non-luminous  flames,  however,  are  far  from  being  adiabatic. 
According  to  Callendar  (B. A.  Reports,  (1910),  214),  10-15  % 
of  the  energy  is  lost  by  radiation,  the  loss  increasing  with 
decreasing  air  supply  and  consequently  increasing  size  of 
flame,  a  maximum  of  15-20  %  loss  being  found  when  a  well- 
defined  inner  cone  is  formed. 

The  radiation  is  ascribed  by  most  investigators  to  the 
intensely  vibratory  condition  of  newly-formed  compound 
molecules  (of  hydrogen  and  oxygen  or  carbon  and  oxygen, 
which  subsequently  revert  to  the  condition  of  ordinary  water 
or  carbon  dioxide  molecules),  a  gas  in  the  ordinary  state  being 
incapable  of  transmitting  radiation.  The  measurements 
of  Helmholtz  (Beiblatter,  14,  (1890),  589)  indicate  that  the 
radiation  from  a  carbon  monoxide  flame  is  some  2*4  times 
that  from  a  similar  hydrogen  flame,  for  equal  volumes  of 
gas  burnt.  This  fact  probably  explains  the  greater 
usefulness  of  carbon  monoxide  than  of  hydrogen  as  a  con- 
stituent of  semi-water  gas  for  heating  purposes,  given  equal 
calorific  values  in  the  two  samples.  The  radiation  from 
flames  is  also  of  considerable  importance  in  connection  with 
the  communication  of  heat  to  the  cylinder  walls  in  gas 
engines. 

An  important  factor  in  the  transmission  of  heat  from 
flames  to  cooler  surfaces  is  the  velocity  of  the  products  of 
combustion  over  the  surface.  Thus,  the  high  temperature 
which  is  obtained  with  a  blow-pipe  in  comparison  with  a 
Bunsen  burner  is  due  in  a  considerable  measure  to  the  high 


GASEOUS  FUELS  299 

velocity  and  consequent  high  degree  of  turbulence  in  the 
gases. 

Calorific  Value  of  Technical  Gas-Air  Mixtures.— 

Reference  to  Table  29  will  show  that  although  a  consider- 
able variation  exists  between  the  calorific  values  of  the 
different  gases,  there  is  much  less  variation  between  the 
corresponding  values  for  the  mixtures  of  the  same  with 
the  volume  of  air  required  for  complete  combustion,  and  since, 
for  most  technical  purposes,  it  is  almost  impossible  to  avoid 
the  use  of  a  certain  excess  of  air,  the  differences  are  still 
smaller  in  actual  practice. 

It  must  not  be  forgotten,  however,  that  a  small  difference 
in  the  calorific  intensity  may  make  a  considerable  difference 
in  the  efficiency,  especially  in  non-regenerative  high  temper- 
ature furnaces.  The  calorific  intensities  are  more  or  less 
in  the  order  of  the  calorific  values  of  the  gas-air  mixtures, 
although  not  necessarily  so ;  thus,  blue  water  gas  has  a 
higher  calorific  intensity  than  coal  gas.  Calculated  values 
have  not  been  given  on  account  of  the  variable  proportions 
of  air  used  in  practice  and  the  lack  of  trustworthy  data 
for  specific  heats  at  high  temperatures. 

Ignition  Temperature. — Mixtures  of  various  inflam- 
mable gases  with  air  or  oxygen  possess,  under  certain  con- 
ditions, quite  definite  ignition  temperatures ;  by  ignition 
temperature  is  meant  the  temperature  at  which  combustion, 
originated  at  a  point,  propagates  itself  rapidly  through  the 
mass  of  the  gas.  In  the  exact  determination  of  such  ignition 
temperatures  there  is  considerable  difficulty  on  account  of 
errors,  such  as  those  caused  by  the  heating  effect  due  to 
slower  initial  combination  at  a  temperature  below  the  true 
instantaneous  ignition  temperature.  The  method  used  by 
Dixon  and  Coward  (Ghent.  Soc.  Trans.,  (1909),  514)  was  to 
spark  the  point  at  which  streams  of  the  two  gases,  separately 
preheated  to  a  given  temperature,  were  brought  together,  and 
their  measurements,  which  are  given  below,  were  criticized 
by  McDavid  (Chem.  Soc.  Trans.,  (1917),  1003)  on  the  above 
grounds.  To  avoid  this  error  and  in  order  to  have  a  station- 
ary volume  of  gas  since  the  mixture  is  imperfect  with  a 


300 


INDUSTRIAL  GASES 


streaming  method,  McDavid  allowed  a  soap  bubble  of  the 
mixed  gases  to  impinge  on  a  wire  electrically  heated  to  a 
given  temperature  ;  his  values  also  will  be  found  below. 
Alternatively,  the  time  factor  can  be  eliminated  by  performing 
the  heating  by  means  of  adiabatic  compression  (Falk). 


TABLE   30. 
IGNITION  TEMPERATURES. 


f*AC 

Gas  +  air. 

Gas  +  oxygen. 
C. 

Dixon  and 
Coward. 

McDavid. 

Dixon  and 
Coward. 

Hydrogen 

580-590 

(10  %  Ht) 

747 

580-590 

Carbon  monoxide  (moist)  .  . 

644-658 

93i 

637-658 

Methane 

650-750 

^> 

IOOO 

556-700 

Ethane          

520-630 

1062 

520-630 

Ethylene 

542-547 

(10  %  C2H4) 

IOOO 

500-519 

Acetylene 

406-440 

— 

416—440 

Sulphuretted  hydrogen 

34°-379 

'      ' 

220-235 

Ignition  temperatures  are  of  importance,  particularly 
in  connection  with  power  production,  as  the  modern  gas  engine 
depends  for  its  high  efficiency  on  the  employment  of  a  high 
degree  of  compression  with  a  correspondingly  high  temper- 
ature production  owing  to  the  adiabatic  compression  (cf. 
p.  346)  ;  it  is,  consequently,  necessary  for  a  suitable  power 
gas  fuel  to  be  capable  of  withstanding  the  required  com- 
pression without  pre-ignition. 

Explosive  Limits  and  the  Velocity  of  Propagation  of 
Explosion. — The  above  are  important  points  in  the  use  of 
fuel  gases,  the  former  from  a  danger  standpoint  (for  values 
for  some  of  the  fuel  gases,  cf.  Table  29),  and  the  latter  in 
relation  to  questions  of  back-firing  ;  thus,  in  burners  of  the 
Bunsen  type  and  in  injector  blow-pipes,  it  is  necessary  for 
the  linear  velocity  of  the  explosive  gas  mixture  to  exceed 
the  velocity  of  propagation  of  explosion  in  the  same. 

Space  will  not  permit  more  than  an  indication  of  the 
complex  nature  of  the  phenomena  of  the  propagation  of  gas 
explosions.  Broadly  speaking,  however,  it  will  suffice  to 


GASEOUS  FUELS  301 

state  that  the  explosion  originating  in  a  tube  results  in  a 
period  of  acceleration  of  the  flame,  succeeded  by  a  more  or 
less  sudden  increase  of  the  velocity  of  propagation  to  a  very 
high  value  of  the  order  of  io,oooft./sec.  The  phenomena, 
particularly  in  the  preliminary  period,  depend  (i)  on  the 
position  of  the  point  of  ignition,  e.g.  whether  near  the  open  or 
closed  end  of  the  tube  ;  (2)  on  the  diameter  of  the  tube, 
and  (3)  on  the  composition  of  the  gas  mixture.  For  further 
information  cf.  Mallard  and  L,e  Chatelier,  Annales  des  Mines, 
[8],  4,  (1883),  524 ;  Dixon,  Phil.  Trans.,  A  200,  (1903),  315, 
and  other  papers. 

Fundamental  Principles  of  the  Production  of  Gaseous 
Fuels  of  Low  Calorific  Value 

Starting  from  the  general  standpoint  that  all  processes 
for  the  complete  gasification  of  coal  depend  on  the  action 
of  oxygen,  or  water,  or  of  both,  on  the  carbon  which  consti- 
tutes the  most  important  part  of  the  coal,  it  will  be  well  to 
consider  the  thermochemical  and  thermodynamical  changes 
involved. 

(i)  Action  of  Air  on  Carbon.— The  combustion  of 
carbon  takes  place  either  to  carbon  monoxide  or  to  carbon 
dioxide  or  to  a  mixture  of  both  according  to  circumstances. 

2C  +  O2  =  2CO  +  58,000  calories  (a) 
C  +  O2  =  CO2  +  97,300  calories  (b) 

Reaction  (a)  corresponds  to  the  liberation  of  2420 
C.H.U./lb.  carbon  (4360  B.T.U.). 

Reaction  (b)  corresponds  to  1he  liberation  of  8110 
C.H.U,/lb.  carbon  (14,600  B.T.U.). 

Now,  the  general  ideal  in  the  production  of  a  fuel  gas  is 
to  have  as  high  a  "  cold  "  thermal  efficiency  as  possible, 
by  which  is  meant  the  ratio  of  the  calorific  value  of  the 
gaseous  fuel  to  that  of  the  corresponding  quantity  of  the  solid 
fuel  from  which  it  originated,  net  values  being  preferably 
taken.  Stated  in  other  words,  the  principle  is  to  transform 
as  little  potential  energy  as  possible  into  "  sensible  "  heat 


302  INDUSTRIAL   GASES 

in  the  gasification  process.  We  shall  see  later  that  in  some 
cases  it  is  feasible  economically  to  utilize  such  "  sensible  " 
heat,  but  in  general  the  gases  are  used  cold,  and  unless 
recovered  by  regenerative  operations,  the  sensible  heat 
liberated  in  the  generator  is  wasted. 

Considering  the  "  cold  "  thermal  efficiency  in  the  above 
reactions,  we  find  that  here  the  case  is  very  simple  since 
carbon  dioxide  is  incapable  of  further  combustion  and  conse- 
quently the  efficiency  will  vary  from 

8no  -  2420  _  5690  _ 
8110         ~~- 


when  only  carbon  monoxide  is  formed,  to  zero  when  all 
carbon  dioxide  is  formed. 

If,  on  the  other  hand,  the  gases  are  utilized  in  the  hot 
state  —  supposing,  for  instance,  that  the  gases  leave  the  gener- 
ator at  a  temperature  of  800°  C.,  about  the  usual  temperature 
—  we  must  add  to  the  heat  of  combustion  of  the  carbon 
monoxide  the  thermal  capacity  of  the  mixture  of  carbon 
monoxide  and  nitrogen. 

Assuming  that  we  are  dealing  with  pure  carbon,  in  which 
case  we  should  have  a  gas  mixture  of  CO  4-  2N2,  and  neg- 
lecting the  increase  in  the  specific  heats  with  temperature, 
we  see  that  the  quantity  to  be  added  is 

785    C»co  X       +  C*N.  X          C.H.U./lb.  carbon 


=  785  (0-242  X  2-33  +  0-243  X  4*66)  C.H.U./lb.  carbon 
=  1330  C.H.U./lb.  carbon. 

The  "  hot  "  efficiency  therefore  equals 

5690  +  1330  =0.866 

8110 

the  difference  from  unity  representing  the  loss  by  radiation 
from  the  generator. 

Up  to  the  present  we  have  been  dealing  with  the  ideal 
case,    viz.    the  production  of    carbon   monoxide   only.     A 


GASEOUS   FUELS  3°3 

consideration  of  the  equilibrium  relations  of  the  reversible 
reaction 

2CO  ^  C  -h  CO2  +  39,3°°  calories 

(cf.  p.  237)  will  indicate  that  this  can  only  be  the  case 
(approximately)  at  temperatures  over  1000°  C.,  although  the 
fact  that  the  partial  pressure  is  approximately  0-33  atm. 
will  hinder  the  decomposition.  According  to  theory  the 
action  of  air  on  carbon  should  result  in  the  production  of  a 
gas  containing  about  33  %  (CO  +  CO2). 

The  following  table  shows  the  equilibria  calculated  from 
the  experimental  data  of  Rhead  and  Wheeler  and  Boudouard 
(cf.  p.  238)  for  various  temperatures  taking  pco  +  pCOz 
equal  to  0-33  atm. 

TABLE   31. 

EQUILIBRIUM  BETWEEN  CARBON  MONOXIDE,  CARBON  DIOXIDE  AND 
CARBON  AT  0-33  ATM.  PRESSURE. 


600 

800 

IOOO 

K  (from  smoothed  curve) 

I4-55 

0-124 

0-00597 

pco  in  atms. 

0-120 

0-318 

0-329 

pco2  in  atms. 
pco/pco2               

0'2IO 
0-57I 

0-012 
26-5 

O'OOI 

329 

An  important  point  in  the  consideration  of  the  attainment 
of  these  equilibria  is  that  discovered  by  Rhead  and  Wheeler 
(loc.  cit.},  namely,  that  the  rate  of  reaction  is  much  greater — 
some  166  times  at  850°  C. — in  the  direction  of  carbon  monoxide 
formation  than  in  that  of  its  decomposition  ;  the  consequence 
is  that  in  passing  through  the  hot  zone  in  the  neighbour- 
hood of  1200-1500°  C.  the  gases  are  practically  free  from 
carbon  dioxide  and  on  subsequent  passage  through  the  upper 
cooler  zones,  the  reaction  in  the  direction  of  dioxide  formation 
is  sufficiently  "  frozen  "  to  prevent  any  considerable  amount 
of  carbon  dioxide  being  formed. 

The  practical  outcome  of  these  considerations  is  that 
from  this  point  of  view  it  is  desirable  to  run  the  producer  at 
as  high  a  temperature  as  possible.  In  practice  this  desider- 
atum is  qualified  by  the  fact  that  much  trouble  is  caused  at 
excessively  high  temperatures  by  "  clinkering  "  and  by  the 


304  INDUSTRIAL   GASES 

increase  in  losses  by  radiation,  etc.  If  the  fuel  used  is 
not  pure  carbon,  but  contains  considerable  quantities  of 
hydrogen,  as  e.g.  bituminous  coal,  the  gaseous  products  will 
contain  appreciable  quantities  of  decomposition  products, 
notably  hydrogen  and  methane,  in  addition  to  carbon 
monoxide,  carbon  dioxide  and  nitrogen. 

(2)  Action  of  Steam  on  Carbon.— As  in  the  case  of 
oxygen,  the  action  of  water  on  carbon  may  take  place  in  either 
of  two  ways  : — 

[C  -f  H2Oliquid  =  CO    +  H2    —  39>7<>o  calories  (a) 

|C  +  H20ga8  =  CO    +  H2    -  29,100  calories  (a1) 

|C  +  2H2OUquid  =  CO2  +  2H2  —  29,500  calories  (b) 

\C  +  2H2Ogas  =  CO2  -f  2H2  —  18,900  calories  (br) 

The  net  calorific  values  of  the  resulting  gaseous  products 
will  be  167  and  102  C.H.U./ft.3  at  15°  C.  respectively  (cf. 
Tables  13  and  29) ;  it  is  therefore  obvious  that  the  product  of 
(b)  is  much  less  desirable  as  a  fuel  and,  consequently,  it  will 
not  be  considered  further.  The  action  differs  from  that  of  air 
in  that  we  have  in  both  the  above  cases,  not  an  evolution 
but  an  absorption  of  heat. 

Thus— 

Reaction  (a)  involves  the  absorption  of  3310  C.H.U./lb.  carbon 

(5960)  B.T.U. 
(«')        „         „  „  2420  C.H.U./lb  carbon 

(4360)  B.T.U. 
,;       (b)        „        „          ,,  2460  C.H.U./lb.  carbon 

(4430)  B.T.U. 

„       (V)       „        „          „  1570  C.H.U./lb.  carbon 

(2830)  B.T.U. 

It  is  therefore  evident  that  the  reactions  cannot  be  self- 
supporting  and  that  the  necessary  supply  of  heat  must  be 
furnished  in  some  way.  External  heating  of  the  generator  is 
impracticable,  and,  consequently,  it  is  found  more  convenient 
to  adopt  the  plan  of  using  the  fuel  itself  and  the  furnace 
lining  as  heat  accumulators  by  supplying  alternately  to  the 
fuel  bed  an  air  blast — the  "  blow  "  period — and  a  steam 
blast — the  "  make  "  period,  or  the  "  run." 


GASEOUS  FUELS  305 

We  have  seen  above  that  the  combustion  of  i  Ib.  of  carbon 
liberates  (a)  2420  C.H.U.  if  carbon  monoxide  be  formed,  and 
(b)  8110  C.H.U.  if  carbon  dioxide  be  formed.  It  will  be 
instructive  to  make  a  rough  estimate  of  the  thermal  balance 
sheet  of  the  generator.  The  calculations  are  made  for  the 
sake  of  indicating  clearly  the  various  items  in  the  heat  balance 
sheet  rather  than  for  obtaining  an  accurate  evaluation  of  the 
coke  requirements.  For  this  purpose  we  will  assume  the 
gases  both  from  the  "  blow  "  and  "  make  "  periods  to  leave 
the  generator  at  a  temperature  of  600°  C.,  and  will  take  no 
account  of  the  increase  in  the  specific  heats  with  rise  of 
temperature,  since  the  calculations  are  only  approximate 
and  the  corrections  are  not  accurately  known  in  all  cases. 
For  further  simplicity  we  will  neglect  the  loss  by  radiation, 
etc.,  from  the  body  of  the  generator  ;  such  losses  vary  with 
the  type  of  generator,  but  may  be  evaluated  for  specific  cases. 

Blow.  (a)  Combustion  to  Carbon  Monoxide. — Heat 
of  combustion  of  12  Ibs.  of  carbon 

=  12  X  2420  C.H.U. 
=  29,000  C.H.U. 

Heat  lost  in  products  of  combustion  (28  Ibs.  CO  and  56  Ibs. 
N2) 

=  585  (0-242  x  28  +  0-243  X  56)  C.H.U. 

=  11,920  C.H.U. 

Total  heat  available  therefore 

=  29,000  —  11,920  C.H.U. 
=  17,080  C.H.U. 

Blow,  (b)  Combustion  to  Carbon  Dioxide. — Heat  of 
combustion  of  12  Ibs.  of  carbon 

=  12  X  8110  C.H.U. 
=  97,300  C.H.U. 

Heat  lost  in  products  of   combustion   (44  Ibs.   CO2  and 
112  Ibs.  N2) 

=  585  (0-202  X  44  4-  0*243  X  112)  C.H.U. 

=  21,120  C.H.U. 
A.  2O 


306  INDUSTRIAL   GASES 

Total  available  heat  therefore 

=  97,300  —  21,120  C.H.U. 
=  76,180  C.H.U. 

For  the  present  purpose  it  will  be  most  convenient  to 
consider  the  reaction  in  the  "  run  "  as  being  carried  out 
with  liquid  water  and  to  add  on  the  heat  carried  into  the 
generator  by  the  steam,  assumed  at  100°  C. 

Make.  —  Heat  supplied  in  18  Ibs.  of  steam,  if  at  100°  C. 

=  18  (85  X  i  +  538)  C.H.U. 
=  11,210  C.H.U. 

Heat  absorbed  in  the  gasification  of  12  Ibs.  carbon 

=  12  X  3310  C.H.U. 

=  39^700  C.H.U. 

Heat  lost  in  the  gaseous  products  (2  Ibs.  H2  and  28  Ibs. 
CO) 

=  585  (3-42  X  2  +  0-242  X  28)  C.H.U. 

=  7960  C.H.U. 

Total  loss  of  heat  therefore 

=  39,700  +  7960  —  11,210  C.H.U. 
=  36,450  C.H.U. 

Considering  the  two  cases  (a)  and  (b)  separately  we  find 
that  the  ratios  of  the  carbon  consumed  in  the  "  blow  "  and 
"  make  "  periods  respectively  would  be  — 

(a}     36,450  _  2-134 
W     17,080          i 

th\     36,450  _  0-478 

W  ^m  =  ~r 

or  the  proportions  of  the  total  carbon  appearing  in  the  useful 
product,  i.e.  water  gas,  would  be  — 


In  actual  practice  the  corresponding  values  are  of  the 
order  of  (a)  0-3,  (b)  0-5-0-6. 


GASEOUS  FUELS  307 

A  simple  calculation  will  indicate  that  i  Ib.  of  carbon  in 
the  "  make  "  period  should  produce  63*0  ft.3  of  water  gas  at 
15°  C.,  or  conversely,  1000  ft.3  of  water  gas  should  require 
15*87  Ibs.  of  carbon  in  the  "  make  "  period.  This  is  equiv- 
alent to  a  total  of 

(a)  15-87/0-319  =  49-7  Ibs.  carbon 

(b)  15-87/0-677  =  23-4  Ibs.  carbon 

per  1000  ft.3  of  water  gas  according  to  the  method  of  com- 
bustion in  the  "  blow  "  period. 

The  average  values  found  in  actual  practice  for  good  work- 
ing are  about  (a)  50-60  Ibs.,  (b)  32  Ibs.  coke,  or,  taking  the  coke 
as  containing,  say,  85  %  carbon,  (a)  42*5-51  Ibs.,  (b)  27  Ibs. 
of  carbon,  the  figures  not  including  the  fuel  for  raising  the 
steam,  this  item,  if  60  Ibs.  steam  used,  being  equivalent 
to  some  7  Ibs./iooo  ft.3  of  water  gas  in  good  boiler  practice. 

If,  as  usually  happens  in  practice,  the  blow  gases  from  a 
generator  working  on  system  (a)  contain  a  certain  proportion 
of  carbon  dioxide,  the  fuel  consumption  may  be  considerably 
lower  than  that  calculated  above. 

Theoretical  considerations  on  the  above  lines  would  point 
to  the  formation  of  the  following  volumes  of  "  blow  "  gases : — 

(a)  3200  ft.3,  (b)  1200  ft.3  per  1000  ft.3  of  water  gas. 

The  volumes  produced  in  practice  are  (a)  3000-4000  ft.3, 
(b)  2000  ft.3. 

Similarly  the  water  requirements  should  be 

I5>8;2Xl8lbs./ioooft.3ati50C. 

=  23-8  Ibs./iooo  ft.3  at  15°  C., 

assuming  complete  decomposition,  which  is  not  realised  in 
practice. 

In  practice  the  weight  required  is  about  60  Ibs.,  including, 
however,  the  steam  for  the  blowers.  If  the  "  blow  "  be 
carried  out  to  give  carbon  dioxide,  the  theoretical  efficiency 
of  the  water  gas  manufacture  should  be  100  %  ;  in  other 
words,  the  net  calorific  value  of  the  water  gas  should  be  equal 
to  that  of  the  coke  used  in  its  manufacture,  assuming  no 
heat  losses  in  the  generator,  blow  gases,  etc.  In  practice, 
however,  the  "  net  cold  "  efficiency  is  of  the  order  of  (a) 
35  %>  (&)  7°  %>  taking  the  net  calorific  value  of  coke  at  8000 


308  INDUSTRIAL  GASES 

C.H.U.  /lb.,  excluding  the  fuel  for  raising  the  steam,  driving 
the  blower,  etc.  Estimate  (a)  neglects,  of  course,  the  calorific 
value  of  the  blow  gases  ;  this,  if  counted,  would  bring  the 
efficiency  up  to  that  of  (b). 

Before  leaving  this  section  of  the  subject,  it  will  be 
instructive  to  calculate  the  effect  of  preheating  the  steam. 
Imagine  the  incoming  steam  to  be  heated  from  100°  C. 
to  600°  C.  at  the  expense  of  the  issuing  water  gas  — 

Heat  absorbed  by  18  Ibs.  of  steam 

=  18  x  500  x  0-473  C.H.U. 
=  4260  C.H.U. 

The  total  heat  loss  during  the  "  make  "  will  therefore  be 
diminished  by  this  amount  and  will  amount  to 

36,450-4260  C.H.U.  =  32,190  C.H.U. 

Therefore  ratio  of  carbon  consumed  in  the  "  blow  "  and 
"  make  "  periods  respectively  is  — 


17,080   i 
b]  32,190  __  0-423 

W  76^85-    — 
Proportion  of  total  carbon  appearing  in  the  water  gas— 

=  °'347 


(b)  =  —  —  =  0703 
1-423 

Total  carbon  required  per  1000  ft.3  of  blue  water  gas 

(a)  15-87/0-347  =  457  Ibs. 

(b)  15-87/0-703  =  22-6  Ibs. 

In  case  (a)  this  value  is  considerably  lower  than  in  that 
previously  considered. 

Thus  far  we  have  considered  the  water  gas  as  being 
composed  of  equal  volumes  of  hydrogen  and  carbon  monoxide. 
In  practice  this  is  approximately  the  case,  but  a  small  percen- 
tage of  carbon  dioxide  is  always  present,  in  amount  depending 


GASEOUS  FUELS 


309 


principally  on  the  temperature  of  the  fuel  bed.  The  reason 
is  to  be  found  in  the  reversible  reaction  known  as  the  water 
gas  equilibrium  : — 

CO  +  H2O  ^  CO2  +  H2  +  10,200  calories. 

The  following  table  indicates  the  results  of  the  equilibrium 

measurements  of  Hahn  (Z.  physik.  Chem.,  42,  (1902),  705  ; 

44,   (1903),  513  ;    48,   (1904),  735),  the  points  being  taken 

from  a  smoothed  curve  which  is  extrapolated  below  686°  C. 

TABLE   32. 
HAHN. — WATER  GAS  EQUILIBRIUM. 


Tempera  ture°C. 
•£  _  pco  •  PHZO 

500 
0-16 

600 
0*32 

700 
0-58 

800 
0*90 

900 
1-25 

1000 

1-62 

1  100 

1-92 

1200 

2-16 

1300 

2-35 

1400 

2-49 

pcoz  .paz" 

The  exact  course  of  the  establishment,  in  technical 
generators,  of  the  above  equilibrium  on  the  one  hand,  and  of 
the  CO,  CO2,  C  equilibrium  on  the  other,  have  been  the  subject 
of  much  discussion.  In  a  discussion  of  the  investigations 
of  Bunte  and  Harries  (/.  Gasbeleucht.,  (1894),  81)  on  the 
results  of  passing  steam  over  carbon  at  different  temperatures, 
and  to  which  we  shall  have  occasion  to  refer  later,  lyUggin 
(/&.,  (1898),  713)  finds  that  the  water  gas  equilibrium  is 
established  at  temperatures  between  760°  C.  and  1000°  C., 
but  that  the  CO,  CO2,  C  equilibrium  is  not  attained,  the 
carbon  dioxide  being  always  in  excess.  It  was  suggested 
by  Haber  that  the  ash  content  of  the  coke  is  operative  in 
facilitating  catalytically  the  attainment  of  the  water  gas 
equilibrium  without  the  carbon  itself  coming  into  equili- 
brium with  the  carbon  monoxide  and  carbon  dioxide. 
Recently  the  question  has  received  experimental  attention 
from  Gwosdz  (Z.  angew.  Chem.,  (1918), i.,  137),  who  found  that 
over  the  range  of  560-855°  C.,  a  considerable  percentage  of 
carbon  dioxide — up  to  29  % — was  always  formed  with  gas 
coke  containing  8-5  %  of  ash.  On  the  other  hand,  with 
almost  pure  carbon — lampblack  with  O'i  %  ash — even  at 
600°  C.,  the  water  gas  contained  only  8'6  %  carbon  dioxide. 


310  INDUSTRIAL  GASES 

Gwosdz's  conclusion  is  that  the  carbon  dioxide  is  not  formed 
in  the  primary  reaction,  but  that  in  the  first  instance  the 
carbon  reacts  with  water  vapour  to  give  carbon  monoxide 
and  hydrogen,  the  establishment  of  the  water  gas  equilibrium, 
in  the  upper  and  cooler  regions  of  the  generator,  following  by 
catalysis  through  the  ash  of  the  fuel. 

In  practical  operation  of  water  gas  plants,  the  temperature 
conditions  are  continually  changing  during  the  "make  "  period 
and  the  duration  of  this  period  is  so  arranged  that  the  average 
percentage  of  carbon  dioxide  does  not  rise  beyond  the  desired 
limit. 

(3)  Action  of  a  Mixture  of  Air  and  Steam  on  Carbon. 
— We  have  seen  above  that  the  action  of  oxygen  on  carbon 
results  in  an  evolution  of  heat  with  a  consequent  tendency 
to  excessive  rise  in  temperature  in  the  producer  while  the 
action  of  water  is  strongly  endothermic,  leading  to  the 
necessity  for  discontinuous  working  and  consequent  lower 
efficiency.  It  is  therefore  not  difficult  to  see  why  a  combin- 
ation of  the  two  processes  has  proved  to  be  the  most  advan- 
tageous method  of  producing  a  fuel  gas  for  furnace  work  and 
for  power  generation.  Such  a  combination  has  the  double 
advantage  of  avoiding  the  tendency  to  "  clinkering  "  and  of 
securing  a  gas  with  less  inert  nitrogen  and  of  higher  calorific 
value  than  air  producer  gas ;  further,  owing  to  the  lower 
temperature,  the  efficiency  is  less  dependent  on  recuper- 
ation of  the  "  sensible  "  heat  of  the  products.  For  a  proper 
understanding  of  the  thermal  balance  it  is  convenient  to 
regard  the  process  as  being  carried  out  in  two  generators, 
disposed  side  by  side,  and  separated  by  a  partition  perfectly 
permeable  to  heat.  If  we  imagine  the  "  blow  "  cycle  of 
the  ordinary  water  gas  manufacture  to  be  carried  out  in 
one  generator  simultaneously  with  the  performance  of  the 
"  make  "  cycle  in  the  other,  the  resulting  gaseous  products 
being  united  giving  "  semi-water  gas,"  it  is  evident  that  we 
have  much  the  same  thermal  balance  as  that  just  worked 
out  for  water  gas  production. 

Thus,  assuming  no  heat-interchange,  the  ratio  of  the 
carbon  reacting  with  water  to  that  reacting  with  air  will 


GASEOUS  FUELS  311 

be  1/2-134,  i.e.  0-32  of  the  carbon  reacts  with  water  and 
0-68  with  air.    The  weight  of  water  per  Ib.  carbon  is  seen  to  be 


Since  the  volume  of  i  Ib.  of  water  vapour  at  100°  C.  is 
26-43  ft.3,  the  volume  of  this  water  at  100°  C.  will  be  26-43  x 
0-48  ft.3  =  12-7  ft.3  Similarly  the  weight  of  the  oxygen 
involved  is  — 

0-68  X  16 
_—  --=0-907  Ib. 

and  the  volume  =  °'9°7  X  1000  ft3  ^        c 

04-50 

=  10-7  ft.3  at  15°  C. 

or      10-7/0-21  ft.3  of  air  at  15°  C.  =  51-0  ft.3  of  air  at  15°  C. 
or  66-0  ft.3  of  air  at  100°  C. 

This  steam/air  ratio  corresponds  to  a  partial  pressure  of 

12*7  X  760 

—  -  —  ,   '       mm.  mercury 
12-7  +  66-0 

=  123  mm.  mercury,  i.e.  a  saturation  temperature  of  56°  C. 

We  have  calculated  for  the  case  of  the  action  of  steam  on 
carbon  that  a  weight  of  49*7  Ibs.  of  carbon  should  produce 
1000  ft.3  of  water  gas  plus  3200  ft.3  of  "  blow  "  gases  (air 
producer  gas)  at  15°  C.,  i.e.  a  total  of  4200  ft.3  of  gas. 
Since  these  data  are  applicable  to  the  present  case,  we  see 
that  1000  ft.3  of  semi-  water  gas  should  result  from  49-7  x 
1000/4200  Ibs.  of  carbon  =  ir8  Ibs.  of  carbon.  The  air 
requirements  per  1000  ft.3  of  gas  should,  therefore,  be 
n-8  x  51  ft.3  at  15°  C.  =  602  ft.3  at  15°  C.,  while  the 
water  is  similarly  evaluated  at  ir8  X  0-48  Ibs.  =  56-6  Ibs. 

If  the  above  ideal  conditions  were  fulfilled,  the  percentage 
composition  of  the  gas,  when  operating  with  pure  carbon 
and  neglecting  carbon  dioxide  formation,  would  be  — 

Hydrogen  .  .          .  .          .  .       11*9 

Carbon  monoxide        ...         .  .       37*3 

Nitrogen  ........       50-8 

lOO'O 


312  INDUSTRIAL   GASES 

corresponding  to  a  calorific  value  (net)  per  ft.3  at  15°  C. 
of  85-6  C.H.U.     On  this  basis  the  thermal  efficiency  would  be 


A  somewhat  lower  saturation  temperature  than  that  just 
calculated  would  be  necessary  in  practice  on  account  of  losses 
due  to  radiation,  convection,  etc.  Owing  to  the  diluting  effect 
of  products  of  distillation  and  partial  replacement  by  carbon 
dioxide,  the  carbon  monoxide  content  is  not  so  high  in 
practice.  By  paying  attention  to  thermal  losses,  effici- 
encies of  about  80  %  may  be  attained  in  actual  working. 

As  regards  the  establishment  of  the  equilibria  in  the 
generator,  the  remarks  on  water  gas  apply  also  to  the  present 
case.  From  a  technical  standpoint,  low  carbon  dioxide 
concentration  is  desirable  in  order  to  secure  high  calorific 
value  and  high  gasification  efficiency.  The  most  important 
condition  for  such  low  concentration  is,  of  course,  the 
maintenance  of  a  high  temperature  in  the  fuel  bed  by  keeping 
down  the  steam  ratio.  On  the  other  hand,  as  we  shall  see 
presently,  it  is  sometimes  advantageous  to  sacrifice  efficiency 
of  gasification  to  the  recovery  of  ammonia,  by  working  with 
a  high  steam  ratio  and  consequent  low  temperature  in  the 
producer. 

Since  the  manufacture  of  semi-water  gas  is  usually 
carried  out  from  bituminous  fuel,  not  from  coke,  there  is 
often  present  in  the  gases  an  appreciable  amount  of  methane 
—  of  the  order  of  3  %  —  formed  mainly  by  destructive  distil- 
lation of  the  fuel  in  the  upper  and  relatively  cool  portions  of 
the  generator. 

A  possible  future  development  of  semi-water  gas  manu- 
facture lies  in  the  substitution  of  pure  oxygen  or  oxygen- 
enriched  air  for  air  in  admixture  with  the  steam  (cf  .  remarks 
on  the  possibilities  in  the  future  provision  of  cheap  oxygen, 
p.  94  and  p.  106).  Using  pure  oxygen,  the  resulting  gas 
would  contain  only  combustibles,  possessing,  in  fact,  the 
advantages  of  water  gas  without  the  inherent  drawback  of 
intermittent  working. 


GASEOUS  FUELS  313 

(4)  Action  of  Carbon  Dioxide  on  Carbon. — There  is 
still  another  method  of  gasifying  carbon,  namely  by  the 
action  of  carbon  dioxide  either  alone  or  in  admixture 
with  air. 

C  +  CO2  =  2CO  —  39,300  calories. 

If  carbon  dioxide  alone  be  passed  through  the  producer, 
the  strongly  endothermic  nature  of  the  reaction,  resulting 
in  an  absorption  of  3270  C.H.U./lb.  carbon  (5890  B.T.U.), 
makes  it  necessary  to  use  an  intermittent  "  blow  "  as  in 
water  gas  manufacture.  Using  a  mixture  with  air,  a  balance 
will  be  struck  as  in  the  case  of  semi-water  gas. 

The  process  was  used  some  years  ago  in  power  production 
on  account  of  the  freedom  from  pre-ignition  troubles  when 
using  this  gas.  A  portion  of  the  gases  from  the  exhaust  of 
the  engine,  which  operates  on  very  high  compression,  is 
returned  together  with  additional  air  to  the  generator.  The 
composition  of  the  gas  is  similar  to  that  of  air  producer 
gas. 


TECHNICAL  PRODUCTION  OF  GASEOUS  FUELS 
OF  LOW  CALORIFIC  VALUE 

AIR  PRODUCER  GAS 

General. — The  gaseous  fuel  resulting  from  the  action 
of  air  on  incandescent  carbon,  and  known  variously  as 
producer  gas,  air  gas,  air  producer  gas,  straight  producer 
gas,  etc.,  was  the  first  form  in  which  carbon  was  completely 
gasified  for  industrial  purposes.  A  simple  form  of  producer 
with  natural  draught  was  introduced  by  Bischof  in  1839, 
but  the  first  important  advance  was  made  by  the  Siemens 
Bros.,  who  used  producer  gas  in  connection  with  the  principle 
of  regeneration  for  steel  melting,  also  introduced  by  them. 
Natural  draught  was  at  first  used,  but  later  air  injection 
was  adopted  and  finally  the  air  was  injected  by  means  of  a 


314 


INDUSTRIAL   GASES 


steam  blast,  air  producer  gas  being  no  longer  used  in  steel 
melting. 

General  Principles  of  Operation. — A  clear  insight 
into  the  principles  governing  the  operation  of  air  producers 
is  afforded  by  Wendt's  investigations  (Stahl  und  Eisen, 
26,  (1906),  1184),  which  were  carried  out  in  a  technical 
generator  using  bituminous  coal  as  fuel,  the  bed  being  7'  3" 
deep.  For  a  summary  of  the  results  obtained,  see  the 
following  table,  which  represents  analyses  of  gases  drawn 
from  different  zones  of  the  producer  at  the  stated  heights 
above  the  grate. 

TABLE   33. 
WENDT'S  EXPERIMENTS  ON  PRODUCER  GAS. 


Height  above 
tuyere. 
Inches. 

Temperature 
°C. 

H2 

CO 

C02 

CH4 

N2 

o 

_ 

_. 

19-6 

8-8 

, 

71-6 

10 

1380 

— 

34*5 

— 

— 

65-5 

20 

— 

— 

34'  5 

0'2 

— 

65-3 

30 

1250 

0-7 

32-7 

0-8 

0-4 

65-4 

40 

— 

11-9 

28-9 

1*0 

2*0 

56-2 

50 

1145 

IO'O 

26-7 

2'0 

3'8 

57-5 

60 

12-3 

27'2 

2'0 

4-2 

54'  3 

Outlet 

610 

6'4 

30-9 

ro 

3-2 

58'5 

Tar  was  present  in  the  gases  at  and  above  the  zone  40"  above  the 
tuyere.     Depth  of  bed  =87". 

An  examination  of  the  above  analyses  will  indicate 
that  the  equilibrium  between  carbon  monoxide  and  carbon 
dioxide  is  established  at  or  below  the  point  20"  above  the 
tuyere. 

Thus,  at  20",  pco2  —  0-002  atm.  (cf.  the  equilibrium 
values  on  p.  303),  the  rate  of  reaction  being  very  high  at  the 
temperature  of  this  zone.  Free  oxygen  is  very  rapidly 
removed  in  the  first  portions  of  the  fuel ;  no  oxygen  was 
found  at  any  of  the  points.  As  the  highly  heated  products 
of  combustion  ascend  through  the  fuel  bed,  their  temperature 
is  lowered  by  contact  with  the  cooler  fuel  and  consequently 
some  reversion  to  carbon  dioxide  takes  place,  but  a  reference 


GASEOUS  FUELS  315 

to  p.  303  will  show  that  equilibrium  is  by  no  means  attained 
at  say  600°  C.,  in  the  time  available. 

Further,  with  the  bituminous  coal  used  in  these  trials,  the 
distillation  taking  place  in  the  upper  regions  results  in  the 
formation  of  methane  and  hydrogen.  The  composition  of 
the  gas  produced  will  vary  with  the  fuel  used  ;  with  coke  the 
hydrogen  and  methane  will,  of  course,  be  lower  than  with 
bituminous  coal. 

The  temperature  of  the  producer  tends  to  rise  until 
limited  by  the  increasing  losses  through  radiation  and  the 
sensible  heat  of  the  gaseous  products ;  the  practical  limit 
is  set  by  the  trouble  of  "  clinkering  "  which  increases  rapidly 
at  high  temperatures,  and  also  by  the  action  on  the  lining  of 
the  producer.  These  difficulties  and  the  low  thermal  effici- 
ency (cf.  p.  302)  have  led  to  the  almost  complete  substitution 
of  semi-water  gas  for  air  producer  gas  except  in  the  case  of 
the  "  blow  "  period  in  the  manufacture  of  water  gas,  where 
the  function  of  the  "  blow  "  is  actually  to  produce  a  high 
temperature  in  the  fuel  bed  and  producer  lining. 

Some  plants  have  been  constructed  with  the  deliberate 
object  of  working  at  the  maximum  possible  temperature  and 
combine  the  production  of  CO2-free  gas  with  the  elimina- 
tion of  "  clinkering  "  difficulties  by  adding  limestone  to 
produce  a  fusible  slag  with  the  ash,  this  slag  being  tapped  off 
regularly  through  a  slag  notch.  According  to  Bone  (Thorpe's 
"Dictionary  of  Applied  Chemistry,"  1912)  a  gas  with  the 
following  percentage  composition  and  a  calorific  value  of 
73  (gross)  or  69  (net)  C.H.U./ft.3  at  15°  C.  is  obtained  with 
the  Thwaite  cupola  producer  using  Lancashire  slack  coal : — 

Hydrogen  5-35 

Carbon  monoxide  . .          . .  29*0 

Carbon  dioxide     . .          . .          . .         2*0 

Methane    . .          2-05 

Nitrogen    . .          . .          . .          . .  61*6 

lOO'OO 

Similar  results  were  obtained  by  Wiirth  and  Co.  (Stahl 
und  Eisen,  (1914),  1135)  using  small  coke,  the  gas  containing 


316  INDUSTRIAL  GASES 

34  %  CO,  1-2  %  CO2,  and  having  a  calorific  value  of  84 
(gross)  or  75  (net)  C.H.U./ft.3  at  15°  C.  The  iron  of  the 
ash  is  stated  to  be  recoverable  with  the  slag  as  a  high  silicon, 
low  sulphur,  pig  iron  (cf.  also  Markgraf,  Stahl  und  Eisen, 
38,  (1918),  703). 

Applications. — Apart  from  its  use  as  a  fuel  gas,  air 
producer  gas  has  some  chemical  applications,  among  which 
may  be  cited  the  manufacture  of  formates,  the  production 
of  nitrogen,  carbon  dioxide  (q.v.}. 

WATER  GAS 

Water  gas  was  first  made  on  an  industrial  scale  in  the 
United  States  in  about  1873,  the  initiation  being  due  to 
lyowe.  No  progress  was  made  in  this  country  until  1888, 
when  a  plant  was  installed  at  the  lyeeds  Forge  operating  on 
the  lyowe  principle,  i.e.  with  the  production  of  carbon 
monoxide  in  the  "  blow  "  period. 

In  order  to  effect  a  distinction  from  carburetted  water 
gas,  really  a  mixture  of  water  gas  and  "  oil  gas  "  (vide  infra), 
water  gas  is  usually  spoken  of  as  "blue  water  gas"  since 
it  burns  with  a  non-luminous  blue  flame. 

General  Principles  of  Operation.— From  what  has 
been  said  in  the  preceding  pages  it  will  be  evident  that  the 
success  of  water  gas  production  depends  on  the  maintenance 
of  a  high  temperature  in  the  fuel  bed  up  to  the  end  of  the 
"  make  "  period.  The  way  in  which  the  CO/CO2  ratio 
varies  with  temperature  is  well  brought  out  by  the  following 
experiments  carried  out  by  Harries  in  Bunte's  laboratory 
(/.  Gasbeleucht.,  (1894),  81),  and  arranged  by  lyUggin  (Ib., 
(1898),  713).  In  these  experiments,  steam  was  passed  over 
wood  charcoal  heated  to  different  temperatures,  on  a  labor- 
atory scale. 

The  values  of  K  in  the  penultimate  column  are  taken  from 
a  curve  representing  the  values  given  in  Table  32. 

Disregarding  certain  experimental  discrepancies,  an 
approximate  agreement  is  seen  to  exist  between  the  calcu- 
lated equilibrium  and  that  observed  experimentally  except 
at  the  lowest  temperature. 


GASEOUS  FUELS 


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318  INDUSTRIAL  GASES 

It  will  be  noticed  that  the  action  at  700°  C.  results  in  the 
formation  of  very  little  carbon  monoxide  and  much  carbon 
dioxide,  while  above  1000°  C.,  only  comparatively  small 
amounts  of  carbon  dioxide  result ;  the  percentage  of  hydro- 
gen, however,  is  not  greatly  affected.  An  important  practical 
pQint  is  the  completeness  of  decomposition  of  the  steam  ; 
this  is  seen  to  be  sufficiently  good  at  1000°  C. 

Water  gas  is  usually  made  from  coke  in  practice,  and 
consequently  its  composition  is  liable  to  less  variation  than 
is  the  case  where  coal,  with  varying  hydrogen  content,  is 
employed ;  for  this  reason  also  the  methane  content  is  low, 
viz.  from  0*1-1*0%.  According  to  Vignon,  the  methane 
content  can  be  increased  to  some  20  %  by  addition  to  the 
coke  of  lime  in  large  quantity. 

The  general  composition  and  characteristics  of  blue  water 
gas  will  be  found  in  Table  29,  p.  297.  According  to  Meade, 
blue  water  gas  usually  contains  about  100  to  120  grains  of 
sulphuretted  hydrogen  per  100  ft.3,  i.e.  0*177-0*194  %  by 
volume,  and  10  to  15  grains  carbon  disulphide  per  100  ft.3, 
i.e.  0*007-0*011  %  by  volume. 

Blue  Water  Gas  Plants 

Generally  speaking,  a  blue  water  gas  generator  consists 
of  a  cylindrical  chamber,  lined  with  fire-brick,  and  provided 
with  a  gas-tight  charging  device  at  the  top  and  with  suitable 
air  and  steam  admission  conduits.  It  is  important  that  the 
steam  should  be  dry,  while  superheating,  preferably  at  the 
expense  of  the  hot-water  gas  leaving  the  generator  if  the 
sensible  heat  of  the  "blow"  gases  is  being  utilized,  is  an 
obvious  desideratum.  Since  the  steaming  is  attended  with 
a  marked  absorption  of  heat,  causing  the  temperature  of  the 
fuel  to  fall  steadily  during  the  run,  the  rate  of  reaction 
rapidly  falls  off  (cf.  Bunte  and  Harries,  Table  34).  It 
would  be  advisable  continuously  to  reduce  the  rate  of  supply 
of  steam,  with  improvement  both  as  regards  heat  losses  and 
the  content  of  carbon  dioxide,  but  this  procedure  is  not 
carried  out  in  practice. 


GASEOUS  FUELS  319 

Owing  to  the  intermittent  character  of  the  bperations 
it  is  necessary  to  provide  a  gas-holder  as  a  balancer  except, 
perhaps,  when  a  battery  of  generators  is  employed. 

Although  attempts  are  made  to  regenerate  heat  from  the 
"  blow  "  gases,  e.g.  in  carburetted  water  gas  manufacture  with 
the  I,owe  system  (vide  infra)  and  from  the  water  gas  by 
superheating  the  steam,  in  the  Dellwik-Fleischer  process,  there 
is  no  doubt  that  much  more  might  be  done  in  this  direction. 

The  Lowe  System  of  Operation. — The  I^owe  system, 
in  which  the  "  blow  "  period  furnishes  air  producer  gas,  is 
the  one  chiefly  adopted  in  this  country,  since  its  application 
to  the  manufacture  of  carburetted  water  gas — for  which 
ultimate  object  most  blue  water  gas  is  produced — admits 
of  economic  utilization  of  the  "  blow  "  gases.  For  working 
on  this  system  the  depth  of  fuel  bed  must  be  fairly  great ; 
a  depth  of  6^  ft.,  according  to  Meade,  gives  the  best  result, 
with  the  coke  not  more  than  3  in.  in  diameter.  The  generator 
is  usually  some  20  ft.  in  total  height.  In  most  producers 
the  steam  is  passed  alternately  up  and  down,  in  order  to  avoid 
chilling  the  bottom  layers  by  the  steam  below  the  temper- 
ature necessary  for  combustion  in  the  "blow"  period; 
in  this  way  a  more  uniform  distribution  is  effected.  The 
"  blow  "  and  "  make  "  periods  in  this  system  of  working  are 
generally  about  3  and  5  minutes  respectively.  The  fuel  con- 
sumed is  usually  about  60  Ibs.  of  coke  per  1000  ft.3  of  blue 
water  gas  inclusive  of  the  fuel  required  for  raising  the  steam. 

According  to  L,ewes,  the  percentage  composition  of  the 
"  blow  "  gases  is — 

Hydrogen  2-5 

Carbon  monoxide  . .          . .      29 

Carbon  dioxide 4 

Nitrogen 64-5 

lOO'O 

while  Meade  gives — 

Carbon  monoxide  . .         . .         . .       17 

Carbon  dioxide 10 

Nitrogen 73 

100 


320  INDUSTRIAL   GASES 

As  stated  above,  the  volume  of  the  "  blow  "  gases  is  some 
3-4  times  that  of  the  blue  water  gas  produced,  about  30  % 
only  of  the  carbon  of  the  fuel  appearing  in  the  water  gas. 

Dellwik-Fleischer  System. — In  view  of  the  low  thermal 
efficiency  (about  35  %)  of  the  I^owe  system  when  used  for  the 
production  of  blue  water  gas  without  regenerative  arrange- 
ments, the  more  rational  system  of  burning  the  carbon 
dioxide  in  the  "  blow  "  period  was  introduced  by  Dellwik 
about  1900  (cf.  Dellwik,  Trans.  Iron  and  Steel  Inst.,  (1900), 
i.,  123).  It  is  used  extensively  on  the  Continent  but  only 
to  a  limited  extent  in  this  country. 

In  this  system  of  working,  a  shallow,  but  frequently 
replenished,  fuel  bed — about  3  ft.  thick — is  employed,  in 
conjunction  with  a  powerful  air  blast,  the  "  blow  "  gases 
containing  some  2  %  carbon  monoxide  (L/ewes) .  As  in  other 
types  of  generator,  the  steam  is  admitted  alternately  at  top 
and  bottom  of  the  fuel  bed,  passing  through  a  heat-inter- 
changer  before  entering  the  generator,  and  so  being  heated 
by  the  effluent  hot-water  gas.  On  account  of  the  much  more 
energetic  liberation  of  heat  in  the  "  blow  "  period,  this 
occupies  only  about  1-2  minutes  while  the  run  lasts  4-8 
minutes. 

According  to  a  test  carried  out  by  Bone,  using  coke  of 
87*4%  carbon  content  (referred  to  the  dry  coke),  34-4  Ibs. 
of  the  dry  coke — 30  Ibs.  carbon — were  required  per  1000  ft.3 
of  blue  water  gas  at  15°  C.  (exclusive  of  fuel  for  raising 
steam),  the  average  percentage  composition  being — 

Hydrogen 49-15 

Carbon  monoxide 42-90 

Carbon  dioxide        3-90 

Methane        . .         . .         . .          . .  0*55 

Nitrogen       3-50 

lOO'OO 

and  the  calorific  value — 


GASEOUS  FUELS  321 

The  "  net  cold  "  thermal  efficiency  was  60*5  %  (excluding 
the  fuel  for  raising  the  steam,  etc.),  50*5  %  of  the  carbon 
appearing  in  the  blue  water  gas. 

Such  high  efficiency  is,  of  course,  not  always  realized 
in  common  practice. 

Kramer  and  Aarts  Process. — The  Kramer  and  Aarts 
process  is  a  modification  of  the  Dellwik-Fleischer  process,  but 
differs  in  the  construction  and  operation  of  the  generator.  Twin 
generators  are  used,  side  by  side,  and  are  operated  as  follows : — 

The  fuel  beds,  of  5-6  ft.  depth,  are  "  blown  "  in  parallel 
for  about  i  minute,  a  powerful  air  blast  being  used.  The 
resulting  gases,  consisting  essentially  of  carbon  dioxide 
and  nitrogen,  pass  out  at  the  top  of  the  generator,  together 
with  secondary  air  to  complete  the  combustion  of  any  carbon 
monoxide  present,  to  a  regenerator  consisting  of  two  vertical 
shafts  arranged  side  by  side,  packed  with  chequer-work 
and  interconnected  at  the  upper  end,  and  then  into  the 
atmosphere.  The  fuel  having  been  raised  to  a  high  tempera- 
ture in  this  way,  steam  is  admitted  at  the  bottom  of  one  of 
the  fuel  beds,  passing  through  the  bed,  up  one  shaft  of  the 
regenerator  and  down  the  other  (the  valve  at  the  top 
communicating  with  the  atmosphere  being  now  closed)  then 
down  through  the  second  fuel  bed  and  escaping  through 
annular  ports  just  above  the  grate.  In  this  way  the  gases 
from  the  generator,  together  with  any  undecomposed  steam, 
are  superheated  in  the  regenerator,  and,  as  relatively  little 
heat  absorption  is  thus  demanded  in  the  second  generator, 
very  complete  decomposition  of  steam  and  elimination  of 
carbon  dioxide  take  place  at  the  resulting  high  temperature, 
the  composition  of  the  gas  suffering  less  impoverishment 
during  the  "  run  "  than  in  other  systems.  After  steaming 
for  some  5  minutes  the  "  blow  "  is  repeated,  and  then 
steaming  is  resumed  in  the  opposite  direction  from  that  of 
the  previous  "  make  "  operation. 

The  Kramer  and  Aarts  system  has  the   advantage  of 

removing   the   gas  from  the  fuel  bed,  i.e.  from   catalytic 

influences,  at  the  highest  temperature  zone,  thus  preventing 

carbon    dioxide    formation  by  reversal  of    the   water  gas 

A.  21 


322  INDUSTRIAL  GASES 

equilibrium,  and  secures  passage  of  the  steam  through  twice 
the  depth  of  fuel  offered  to  the  passage  of  the  air.      In  a 
recent  test  of  a  Kramer  and  Aarts  plant  by  Bone,  using 
coke  of  87-2  %  carbon  content  (referred  to  the  dry  coke), 
the  following  data  were  obtained  : — 

Dry  coke  per  1000  ft.3  of  gas  at  15°  C.  =  287  Ibs.  =25-0 
Ibs.  carbon,  exclusive  of  the  fuel  required  for  raising  the  steam. 
The  average  percentage  composition  of  the  gas  was — 
Hydrogen      . .          . .          . .          . .     45-10 

Carbon  monoxide     . .          . .          . .     4370 

Carbon  dioxide         . .          . .          . .       375 

Methane        . .          . .          . .          . .       0*50 

Nitrogen        . .       6-95 

and  the  calorific  value —  loo'oo 

Gross     ..         ..     162  jCHU/ft3at      oc 
Net        . .          . .     149  $ 

The  "  net  cold  "  thermal  efficiency  was  0705  (excluding 
the  fuel  used  for  raising  the  steam).  6o'6  %  of  the  carbon 
in  the  fuel  appeared  in  the  water  gas. 

Figures  are  also  given  by  Keable  (/.  Soc.  Chem.  Ind., 
(1918),  644  A) ;  29*8  Ibs.  of  coke  were  required  per  1000  ft.3 
of  blue  water  gas.  Carburetted  water  gas  may  be  produced 
with  this  plant  if  desired,  the  oil  being  sprayed  into  the 
second  generator. 

Carburetted  Water  Gas 

One  of  the  chief  applications  of  water  gas  is  as  an  inter- 
mediate product  in  the  manufacture  of  carburetted  water 
gas  for  the  purpose  of  addition  to  coal  gas.  Carburetted 
water  gas  is  really  a  mixture  of  blue  water  gas  and  "  oil  gas," 
meaning  by  the  latter  term  the  products  of  "  cracking  " 
petroleum  oils  at  a  high  temperature.  For  the  production 
of  this  mixture,  the  Lowe  system  is  well  suited,  and  the 
carburetted  water  gas  in  this  country  is  principally  made  by 
this  system,  the  best  known  plant  being  that  of  Humphreys 
and  Glasgow,  an  American  firm. 

Briefly  described,  the  process  is  carried  out  in  the  follow- 
ing manner.  The  hot  "  blow  "  gases,  consisting  mainly  of 


GASEOUS   FUELS  323 

• 

carbon  monoxide  and  nitrogen,  are  led  to  a  "  carburettor  " 
down  which  they  pass,  a  supply  of  secondary  air  being 
admitted  at  the  top.  The  carburettor  consists  of  a  chamber 
packed  with  chequer- work,  which  is  heated  to  a  high  temper- 
ature by  the  combustion  of  the  "  blow  "  gases.  I/caving 
the  carburettor  the  gases  pass  up  a  tall  "  superheater  " 
chamber  about  twice  the  height  of  the  carburettor,  also 
packed  with  chequer-work,  a  further  supply  of  air  being 
admitted  to  complete  the  combustion  of  the  carbon  dioxide ; 
the  products  finally  escape  into  the  stack.  During  the 
"  run  "  the  blue  water  gas  passes  through  the  chambers  in 
the  same  direction.  Oil  is  sprayed  into  the  carburettor  at 
the  top  mostly  during  the  first  half  of  the  "  run,"  so  as  to  be 
swept  out  before  the  next  "  blow  " ;  in  passing  down  this 
chamber  and  up  the  "  superheater  "  the  oil  vapours  are 
converted  into  gaseous  products  by  contact  with  the  brick- 
work, heated  to  about  750°  C. 

The  mixed  gases  from  the  top  of  the  "  superheater  " 
are  led  to  sulphuretted  hydrogen  and  carbon  dioxide  purifiers. 
The  sulphur  content  is  much  less  than  that  of  crude  coal  gas, 
and  although  naturally  variable  maybe  about  100  grains  H2S 
per  100  ft.3  (0-16  %  by  volume) ;  the  sulphur  is,  moreover, 
mostly  in  the  form  of  sulphuretted  hydrogen  which  is  re- 
movable by  iron  oxide,  the  final  sulphur  content  (CS2)  being, 
according  toMeade,  10-15  grains  per  100  ft.3.  The 'Composi- 
tion of  the  carburetted  water  gas  is  naturally  dependent  on 
the  proportion  of  oil  used,  generally  about  2-3  gallons  per  1000 
ft. 3  of  carburetted  water  gas.  It  is  not  usual  to  add  more  than 
one  volume  of  carburetted  water  gas  to  two  volumes  of  coal  gas, 
in  order  to  keep  down  the  final  percentage  of  carbon  monoxide, 
most  town  gas  containing  15-30  %  of  carburetted  water  gas. 
The  coke  consumption  is  usually  of  the  order  of  45  Ibs.  of 
coke  per  1000  ft.3  of  carburetted  water  gas,  inclusive  of  the 
fuel  for  raising  the  steam.  According  to  Meade  (/.  Gas 
Lighting,  117,  (1912),  211),  the  coke  for  the  generator  is  about 
37  Ibs.  coke/iooo  ft.3  of  carburetted  water  gas  in  good  practice, 
lyewes  states  that  the  thermal  efficiency  of  the  process  may  be 
as  high  as  80  %,  Meade  gives  61  %.  Table  29  gives  a 


324  INDUSTRIAL  GASES 

typical  example  of  the  composition  of  carburetted  water 
gas,  the  calorific  value  of  which  is  usually  about  300  gross, 
275  net  C.H.U./ftA 

Originally  used  as  an  enricher  on  account  of  its  high 
illuminating  power  when  burnt  in  a  batswing  burner — 
according  to  Meade  about  18  C.P.  as  compared  with  14  for 
coal  gas — carburetted  water  gas  is  now  used  principally  as 
a  means  of  coping  with  "  peak  "  and  emergency  loads  in 
municipal  gas  supply  stations  on  account  of  the  ease  and 
speed  with  which  the  plant  can  be  started  up,  and  of  the  small 
standby  costs  of  producer  plant  in  comparison  with  coal  gas 
retorts,  a  bench  of  which  requires  about  three  days  for 
heating  up.  Carburetted  water  gas  is  even  used  for  distri- 
bution without  admixture  in  the  United  States. 

Recently,  owing  to  the  difficulty  of  obtaining  oil  on 
account  of  the  decreased  tonnage  and  the  demands  of  the 
Navy,  together  with  the  tendency  towards  the  replacement 
of  the  illuminating  standard  by  a  calorific  standard,  blue 
water  gas  (i.e.  uncarburetted)  has  sometimes  been  added,  e.g. 
20  %,  to  coal  gas.  Such  addition  has  previously  been 
regarded  with  disfavour  in  this  country,  where  the  percentage 
of  carbon  monoxide  in  illuminating  gas  does  not  often  exceed 
1 6  %,  on  account  of  the  poisonous  properties  of  blue  water 
gas  with  its  high  carbon  monoxide  content. 

The  Humphreys  and  Glasgow  plant  at  the  Beckton  works 
of  the  Gas,  Light  and  Coke  Co.  produces  some  18  million 
ft.3/day  of  carburetted  water  gas  and  consists  of  twin  genera- 
tors which  can  be  operated  in  series  or  in  parallel  according 
as  to  whether  the  quality  or  the  quantity  of  the  gas  is  of 
more  importance. 

In  the  Humphreys  and  Glasgow  and  other  plants,  special 
interlocking  devices  are  used  to  prevent  the  formation  of 
explosive  mixtures,  etc. 

The  carburetting  of  water  gas  may  also  be  performed  by 
the  "  cold  "  process,  i.e.  by  the  addition  of  benzol,  this 
process  being  specially  suitable  when  the  "  blow  "  gases 
consist  of  carbon  dioxide  and  nitrogen  only. 

Various  proposals  have  been  made  for  combined  systems 


GASEOUS  FUELS  325 

effecting  both  destructive  distillation  of  the  coal  and 
subsequent  complete  gasification  of  the  coke  with  the  aid  of 
steam  in  the  lower  part  of  the  same  generator,  the  gaseous 
products  being  mingled  except  as  regards  the  "  blow  "  gases 
from  the  water  gas  production. 

Applications  of  Blue  Water  Gas 

As  explained  above,  the  chief  application  of  blue  water 
gas  is  in  connection  with  the  manufacture  of  carburetted 
water  gas.  It  is,  however,  used  in  large  quantities  for 
heating  purposes  and  in  particular  for  the  welding  of  large 
steel  tubes  and  plates,  as  its  flame  is  short  and  of  high  calo- 
rific intensity,  slightly  greater  than  that  of  coal  gas.  Using 
preheated  air  it  is  even  possible  to  melt  platinum.  Some 
care  is  needed  by  reason  of  its  poisonous  properties  and 
absence  of  smell,  strongly  smelling  substances  such  as 
mercaptan  sometimes  being  added  to  mitigate  this 
danger.  Blue  water  gas  is  also  used  in  large  and  increasing 
quantities  for  the  manufacture  of  hydrogen  by  the  I/ane  and 
other  allied  processes,  by  the  B.A.M.A.G.  continuous 
catalytic  process,  etc.  Blue  water  gas  is  seldom  used  in 
internal  combustion  engines  on  account  of  its  liability  to 
pre-ignition,  but  may  be  used  if  the  compression  is  not  too 
high.  To  a  limited  extent,  blue  water  gas  is  used  in  furnace 
work,  but  is  not  so  convenient  for  general  purposes  as  semi- 
water  gas,  cf.  also  the  remarks  on  p.  298  anent  the  bearing  of 
high  hydrogen  content  on  the  radiation  from  flames.  On  a 
pre-war  basis  blue  water  gas  could  be  manufactured  at  a  cost 
as  low  as  4^./iooo  ft.3  and  carburetted  water  gas  at  about 
8d./iooo  ft.3. 

SEMI-WATER  GAS 

General. — The  subject  of  semi-water  gas,  by  which 
general  term  we  will  denote  the  products  depending  on  the 
action  of  a  mixture  of  air  and  steam  on  incandescent  carbon, 
is  somewhat  complex  owing  to  the  variety  of  the  ultimate 
objects  of  plants  in  which  the  essential  reaction  is  the  above. 

Generally  speaking,  semi-water  gas  plants  may  be  divided 
into  two  classes  :  (i)  those  operating,  usually  on  bituminous 


326  INDUSTRIAL  GASES 

coal,  for  the  production  of  a  gas  which  is  used  directly,  in 
the  hot  state  without  any  recovery  of  ammonia  or  other 
products,  for  furnace  operations  ;  (2)  those  operated  princi- 
pally for  the  production  of  power. 

General  Principles  of  Operation 

Perhaps  the  most  important  variables  as  regards  general 
procedure  in  the  manufacture  of  semi-water  gas  are  (i)  the 
nature  of  the  fuel ;  (2)  the  saturation  temperature  of  the 
air  blast,  i.e.  the  ratio  of  oxygen  to  steam;  and  (3)  the  rate 
of  gasification  per  square  foot  of  grate  area. 

(i)  Choice  of  Fuel. — The  statement  already  made  as  to 
the  possibility  of  utilizing  almost  any  type  of  low  grade  fuel 
in  a  producer  applies  particularly  to  the  manufacture  of 
semi-water  gas.  This,  however,  should  not  be  taken  as 
meaning  that  the  nature  of  the  fuel  has  no  technical  impor- 
tance ;  on  the  contrary,  it  is  a  very  important  consideration 
in  the  design  and  performance  of  producers. 

Of  special  importance  are  the  caking  propensities  of  the 
fuel,  which  determine  the  tendency  to  choking  and  channelling 
and,  if  highly  developed,  make  the  use  of  the  fuel  in  a  producer 
out  of  the  question ;  the  nature  and  quantity  of  the  ash, 
which  affect  the  difficulty  of  clinkering  and  the  permissible 
temperature  as  determined  by  the  air /steam  ratio  ;  and  the 
carbon  content,  which  influences  the  physical  properties  of 
the  fuel  and  the  composition  of  the  resulting  gases,  the 
calorific  value  varying  with  the  proportion  of  volatile  hydro- 
carbons in  the  fuel. 

An  adequate  treatment  of  the  complex  subject  of  the 
classification  of  solid  fuels  is  beyond  the  scope  of  the  present 
volume,  but  a  brief  indication  of  the  different  varieties  of 
coal  is  desirable.  A  very  complete  synopsis  of  the  avail- 
able literature  on  the  subject  of  the  constitution  of  coal  will 
be  found  in  a  monograph  by  Stopes  and  Wheeler,  published 
by  the  Department  of  Scientific  and  Industrial  Research, 
1918.  Many  attempts,  none  wholly  successful,  have  been  made 
to  correlate  the  properties  of  coals  with  their  compositions. 

A  classification  due  to  Campbell  (Trans.   Amer.  Inst. 


GASEOUS  FUELS  327 

Mining  Engineers,  36,  (1906),  324),  and  adopted  by  the  United 
States  Geological  Survey,  is  given  below  : — 

Group.  C  :  H  ratio. 

A.       Graphite  ..  oo     -(?) 

Anthracite 

D.  Semi-anthracitic  . .         26(?)-23(?) 

E.  Semi-bituminous  . .         23(?)-20 

20    -17 

Bituminous 


.  \ 


I. 


17    -14-4 


I2-5-II-2 


J.       lignite     ..          ..         ..         11-2-9-3 

K.      Peat  ..  9-3-(?) 

Iv.      Wood,  Cellulose  . .  7-2 

According  to  Seyler's  classification  the  carbon  content 
works  out  as  follows  : — 

Class     . .    Anthracitic  Carbonaceous  Bituminous  I4gnitous 

Pofrcearbonel>93-3  W^r*          91*84          84-75 

the  carbon  being  reckoned  on  the  pure  coal  substance  free 
from  ash  and  sulphur. 

An  important  characteristic  of  coals,  especially  of  bitu- 
minous coals,  is  the  variation  in  their  properties  as  regards 
"  caking  "  or  agglomeration  on  heating  in  absence  of  air. 
The  exact  relation  between  this  property  and  the  composition 
is  not  definitely  established  ;  it  may,  however,  be  stated  that 
bituminous  coals  may  be  classified  roughly  in  the  order 

non-caking 

caking 

coking 
according  to  the  decrease  of  the  carbon/hydrogen  ratio. 

Nitrogen  Content  of  Coal. — The  percentage  of  nitrogen 
present  in  coal  varies  somewhat,  but  is  usually  about  1*3- 
1'5  %•  This  is  equivalent  to  35-41  Ibs.  N2/ton  coal,  or 
137-158  Ibs.  ammonium  sulphate/ton  coal.  It  is  evident  that 
with  a  possible  70  %  recovery  of  this  nitrogen  the  quantities 
of  ammonia  capable  of  production  would  be  very  large  if  any 


328  INDUSTRIAL  GASES 

considerable  proportion  of  the  fuel  consumed  were  gasified 
under  suitable  conditions.  Thus  70  %  recovery  at  1*3  % 
nitrogen  is  equivalent  to  96  Ibs.  ammonium  sulphate/ton  coal, 
the  value  of  which  sulphate  is  an  important  fraction  of  that  of 
the  fuel. 

Sulphur  Content  of  Coal. — Sulphur  is  present  to  the 
extent  of  0-5-2-5  %  in  coal,  partly  in  combination  with  the 
mineral  constituents  of  the  ash,  e.g.  FeS2,  CaSO4,  and  partly 
in  the  form  of  organic  compounds.  The  latter  volatilize 
on  heating,  but  the  bulk  of  the  sulphur  remains  in  the  coke 
on  destructive  distillation. 

Other  Deleterious  Constituents  of  Coal. — Coal  contains  small 
quantities  of  arsenic  and  phosphorus ;  arsenic  may  be 
present  to  the  extent  of  some  O'Oi  %  by  weight  (cf.  Wood, 
Smith  and  Jenks,  /.  Soc.  Chem.  Ind.,  (1901),  437). 

An  important  point  in  the  choice  of  fuel  for  a  particular 
object  is  the  question  of  tar  elimination.  The  tar  produced 
with  different  fuels  varies  not  only  in  quantity  but  also  in 
quality,  the  property  of  chief  importance  from  our  point  of 
view  being  the  ease  of  removal  of  the  fog,  which  is  particularly 
injurious  when  the  gas  is  to  be  used  in  internal  combustion 
engines  owing  to  its  deleterious  action  by  deposition  on  the 
valves,  etc.  Thus,  in  spite  of  the  small  proportion  of  volatile 
matter  in  coke,  the  tar  fog  produced  in  the  generator  is 
specially  difficult  to  scrub  out.  For  such  reasons,  in  order 
to  avoid  the  use  of  elaborate  scrubbers,  etc.,  anthracite  is 
usually  employed  in  preference  to  the  much  cheaper  bitumi- 
nous coal  in  relatively  small  "  suction  "  power  gas  plants, 
Generally  speaking,  however,  bituminous  coal  is  the  usual 
fuel  for  semi- water  gas  production  on  a  large  scale. 

(2)  The  Saturation  Temperature  of  the  Blast.— 
In  our  preliminary  examination  of  this  question  we  arrived 
at  a  saturation  temperature  of  56°  C.  as  striking  the  thermal 
balance  for  the  ideal  case  considered.  In  practice,  however, 
it  is  possible  to  operate  over  a  considerable  range  of  the 
oxygen/steam  ratio  according  to  the  quality  of  gas  required 
and  the  degree  of  regeneration,  if  any,  of  the  sensible  heat 
carried  off  by  the  gases. 


GASEOUS  FUELS  329 

A  valuable  large-scale  investigation  of  the  conditions 
influencing  the  production  of  semi-water  gas  was  carried 
out  by  Bone  and  Wheeler  (Trans.  Iron  and  Steel  Inst.,  (1907), 
i.,  126  ;  (1908),  iii.,  206),  using  a  Mond  type  of  producer  with 
Lancashire  bituminous  coal.*  The  main  results  of  the 
investigation  are  summarized  in  Table  35. 

Among  the  more  important  conclusions  from  this  investi- 
gation may  be  mentioned  the  following :  (cf .  also  synopsis 
of  the  same  by  Bone  in  his  article  on  Fuel  in  Thorpe's 
"  Dictionary  of  Applied  Chemistry,"  1912)  : — 

(1)  The  mean  final  distribution  of  the  carbon  of  the  coal 
is  as  follows  : — 

In  the  gas 92^4  % 

„     tar 6-3% 

„     ash 1-3  % 

lOO'O 

(2)  The  steam  undergoes  practically  complete  decompo- 
sition at  saturations  up  to  55°  C.,  above  which  temperature 
some  steam  passes  through  the  fuel  though  the  absolute 
quantity  decomposed  per  unit  weight  of  fuel  increases.   This  is 
due  to  the  endothermic  nature  of  the  carbon-steam  reaction 
which  causes  a  lowering  in   temperature  in  the  fuel  bed 
until  such  tendency  is  balanced  by  the  falling  rate  of  reaction. 

(3)  Increasing  the  depth  of  the  bed  beyond  3^  ft.  and 
doubling  the  rate  of  gasification  have  little  influence  on  the 
quality  of  the  gas. 

(4)  The  degree  of  saturation  has  no  great  effect  on  the 
"  net  cold  "  thermal  efficiency  (including  the  fuel  required 
for  raising  the  steam)  except  when  the  saturation  temper- 
ature exceeds  60°   C.     Above  this  temperature   a  steady 
decline  is  observed.      The   authors  conclude  that  the  best 
compromise    between    high    thermal    efficiency    and    the 
production  of  a  good  furnace  gas  with  high  carbon  monoxide 
content  is  obtained  at  45-55°  C.,  consequently  50°  C.  would 
appear  to  be  about  the  best  saturation  temperature  (cf.  also 

*  For  similar  experiments  cf.  also  Neumann,   Stahl  und  Eisen,  33, 
(1913),  394- 


330 


INDUSTRIAL   GASES 


TABLE   35. 
BONE  AND  WHEELER'S  EXPERIMENTS 


Average  depth  of  fuel  bed    .  .          .  .          .  .                      3  ft.  6  in. 

Average  rate  of  gasification  (day  shift)  per  "I                           .         , 
hour  per  producer      J 

Steam  saturation  temperature  °C.  .  . 

45 

50 

55 

60 

70 

H2 
CO 
Percentage  composition      CO2 
CH4 

Na 

Total  percentage  of  combustibles 

11-60 
31*60 
2'35 
3'°5 
51-40 

12-35 
30-60 
2-50 
3-00 

5i'55 

I5-45 
28-10 
4-40 
3-00 
49'05 

i5'5° 
27-30 
5-10 
3*05 
49-05 

45^5 

I9-75 
20-85 

9-25 
3'45 
46-70 

46*2 

49-95 

46-6 

44^5 

Calorific  value,  C.H.U./ft.8  \  Gross 
at  15°  C.                            /  Net  .  . 

94-8 
89-8 

94-0 
88-8 

95'2 
89*0 

94'  i 

87-9 

92-4 

84-8 

Coal  used  per  TOGO  ft.3  of  gas  at  15°  C.    Lbs. 

I5'9 

16-0 

16-0 

157 

— 

Steam  added  to  blast.     Lbs.  per  Ib.  coal  .  . 

0'2 

0'2I 

0-32 

°"45 

— 

Percentage  steam  decomposed 

all 

all 

all 

76-0 

— 

Total  percentage  carbon  losses  (tar,  ashes, 
soot)           

7'3 

7'9 

9-I5 

8-0 

— 

Air  used  per  Ib.  coal.     Ft.3  at  15°  C. 

40-9 

40-7 

38-77 

39'  5° 

— 

-.  ,  .       ,  oxygen  from  steam  . 
Ratio  of  —  ^°                  —  .     -m  the  semi- 
oxygen  from  air 

water  gas    .  .          .... 

o'33 

o*3 

0*42 

°'44 



Net  cold  thermal  efficiency  as  in  trials,* 
including  steam  for  blowers 

°'73 

0-718 

0-722 

0*725 

— 

Ditto,*  including  also  steam  for  the  washers 

— 

— 

— 

— 

— 

Net  cold  thermal  efficiency  including  fuel 
for  raising  the  steam  for  the   blast   (if 
boiler  efficiency  =70  per  cent.),  also  steam 
for  the  blowers  and  washers 

Ammonia  in  the  gases.    Lbs.  ammonium  sul- 
phate/ton coal 

— 

— 

— 

— 

— 

*  In  the  actual  trials  exhaust  steam  was 


GASEOUS  FUELS 


ON  SEMI- WATER  GAS  PRODUCTION. 


7  ft. 
1  1  '5  cwt. 

60 

65 

70 

75 

so 

1  6-  60 
27-30 
5'25 
3*35 
47*5° 

18-30 
25-40 
6'  95 
3*4° 
45-90 

19-65 
21-70 

9-15 
3-40 
46-10 

21-80 

18-35 
11-65 

3'35 

44-85 

22-65 
16-05 

I3'25 
3-50 
44'55 

47*25 

47-10 

4475 

43'50 

42-2 

97'7 
91-1 

97-6 
90*6 

93-5 
86-0 

90-6 

82-8 

89-3 
8i'3 

T5'4 

15-8 

15-0 

14-6 

14-4 

0'45 

0'55 

0-80 

no 

i-55 

87-0 

80-0 

6ro 

52-0 

40-0 

5'8 

7-8 

8-1 

r  i 

8-4 

38-98 

36-8 

36-7 

38-9 

39-1 

0-50 

0*62 

0-65 

0-75 

0-80 

0778 

0-750 

0-727 

0-701 

0-665 

0-715 

0-687 

0-660 

0-640 

0*604 

0-687 

o"655 

0-630 

0-611 

0-578 

39'° 

447 

5i'4 

65-25 

71-8 

used  except  at  the  saturations  over  65°  C. 


332  INDUSTRIAL  GASES 

Voigt,  /.,  Gas  Lighting,  109,  (1910),  168).  For  this 
temperature,  at  which  it  is  found  possible  to  operate 
continuously,  the  gas  has  the  percentage  composition  — 

Hydrogen      ......  12*35 

Carbon  monoxide    .  .          .  .  30*60 

Carbon  dioxide        .  .         .  .  2*50 

Methane        ......  3-00 

Nitrogen        ......  51-55 

Attention  is  drawn  to  the  importance  of  the  fact  that 
when  used  for  regenerative  furnaces  the  gas  entering  the 
regenerators  should  be  of  such  composition,  including  its 
moisture  content,  that  no  change  should  be  set  up  by  establish- 
ment of  the  water-gas  equilibrium  (at  any  rate  in  the  direction 
of  converting  carbon  monoxide  into  carbon  dioxide  by  reason 
of  the  presence  of  too  much  water  vapour)  at  the  temperature 
in  question,  namely  about  1100-1200°  C.  Thus,  the  gas 
obtained  at  50°  C.  saturation  temperature  of  the  blast,  when 
saturated  with  water  vapour  at  20°  C.,  and  having  conse- 
quently a  composition  of 

Hydrogen      .  .  .  .  .  .  12*1 

Carbon  monoxide  .  .  .  .  29*9 

Carbon  dioxide  .  .  .  .  2*4 

Methane        .  .  .  .  .  .  2*9 

Nitrogen        .  .  .  .  .  .  50-4 

Water  vapour  .  .  .  .  2*3 

lOO'O 

gives  a  value  of 

K  ^29-9  x  2-3 
2'      X  I2'I 


approximately  equal  to  that  corresponding  to  the  regener- 
ator temperature  (cf.  Table  32),  and  is  found  to  pass 
unchanged  through  the  regenerator. 

(5)  The  methane  content  is  independent  of  the  steam/  air 
ratio,  indicating  that  its  presence  is  due  mainly  to 
destructive  distillation. 


GASEOUS  FUELS 


333 


The  actual  proportion  of  steam  used  in  practice  will 
depend,  of  course,  on  the  moisture  content  of  the  fuel,  thus, 
peat  may  require  no  addition  of  steam,  while  lignite  requires 


120 


110 


0,100 
k 

5  90 
§ 


80 


88 

!- 

$60 

K 

§  50 


03 

I4 

5 


30 


20 


10 


0-15 
0-14 

0'I3| 

x 

0-12  § 


Ollg 
§ 

o-ios 


0-9  fc 


0-7 

O 
-06Q: 


-0-5 
04 
0-3 
0-2 
0-1 


0        10      20      30     40      50      60      70      80      90     MOO 
TEMPERATURE  OF  SATURATIONS 

FIG.  23. — Curve  giving  water  content  of  air  blast  for  saturation  at 
different  temperatures. 

relatively  little.  As  seen  in  the  production  of  air  producer 
gas,  it  is  advantageous  from  the  point  of  view  of  low  carbon 
dioxide  content,  to  run  at  a  temperature  not  below  1000°  C., 
but,  on  the  other  hand,  high  working  temperatures  involve 


334 


INDUSTRIAL   GASES 


greater  losses  of  sensible  heat  in  the  gases  and  of  heat  by 
radiation,  and  also  give  rise  to  clinkering  troubles.  The 
steam/air  ratio  will  consequently  depend  on  the  nature  of 
the  ash,  its  quantity  and  fusibility,  and  incidentally  on  the 
type  of  grate,  depth  of  ash,  etc.  Fig.  23  gives  the  relation 
between  the  saturation  temperature  and  the  proportion  of 
steam  present  in  the  blast. 

For  very  low  grade  fuels  with  high  ash  content  special 
producers  are  constructed. 

(3)  The  Rate  of  Gasification.— In  the  above  cited 
experiments  by  Bone  and  Wheeler  the  rate  of  gasification  was 
as  high  as  35  lbs./hour/ft.2  grate  area,  and  a  similar  perform- 
ance is  claimed  in  the  "  Alma  "  producer — modified  Mond 
type — designed  by  them. 

The  rates  attained  in  usual  working  are,  however,  more  of 
the  order  of  15  lbs./hour/ft.2  grate  area. 

The  nature  of  the  reactions  taking  place  in  the  generator 
is  well  illustrated  by  the  experiments  carried  out  by  Wendt 
on  a  technical  semi-water  gas  producer  with  a  fuel  bed 
of  7j  ft.  depth. 


TABLE    36. 
WENDT'S  EXPERIMENTS  ON  SEMI-WATER  GAS  PRODUCTION. 


Height  above 
tuyere. 
Inches. 

Temperature 

H2 

CO 

C02 

CH4 

N2 

02 

0 

__ 

__ 

. 

11-4 

__ 

79-1 

9-5 

10 

mo 

10-5 

22'0 

9-3 

0-4 

57'5 

— 

20 

— 

IS'? 

28-0 

5-5 

0-9 

51-9 

— 

30 

925 

17-9 

32-7 

3-0 

F2 

45'2 

— 

40 

2r8 

28-7 

5*o 

5'0 

39'5 

— 

50 

810 

20-7 

28-3 

6-0 

4*8 

40-2 

—  • 

00 

— 

19-0 

28-0     |       5-3 

4'1 

4J6 

— 

Outlet 

440 

14-6 

26-8            5-5 

3'4 

49'7 

~ 

Tar  was  present  at  and  above  the  zone  40  in.  above  the  tuyere.     Depth 
of  fuel,  7'  5*. 

It  will  be  noted  that  the  temperatures  are  considerably 
lower  than  those  in  the  corresponding  tests  in  the  same 
generator  in  the  absence  of  steam  (p.  314).  The  carbon 


GASEOUS  FUELS  335 

monoxide  concentration  rises  to  a  maximum  and  the  carbon 
dioxide  concentration  falls  to  a  minimum  at  30  in.  above  the 
tuyere,  the  less  favourable  water  gas  equilibrium  at  the  lower 
temperature  in  the  upper  regions  causing  conversion  of 
monoxide  into  dioxide.  Methane  and  hydrogen  are  given 
off  in  the  upper  layer  from  the  bituminous  fuel,  much  of  the 
sensible  heat  of  the  gases  being  absorbed  in  the  process  of 
distillation. 

Semi-Water  Gas  Plants 

General. — The  plants  for  the  production  of  semi- water 
gas  may  be  described  under  the  two  general  headings  of 
pressure  plants  and  suction  plants  according  as  the  pressure 
in  the  generator  is  greater  or  less  than  atmospheric.  Pressure 
plants  are  used  for  all  furnace  gas  production  and  for  most 
large  power  installations  (over  about  500  H.P.),  while 
suction  plants  are  convenient  for  relatively  small  power 
plants. 

Pressure  Plants. — A  pressure  gas  plant  consists 
essentially  of  a  vertical  cylindrical  shaft  lined  with  firebrick, 
having  a  fuel  bed  usually  about  3-7  ft.  in  depth,  and  suitable 
arrangements  for  charging  from  the  top,  e.g.  by  the  use  of 
a  double  cone  hopper,  without  loss  of  gas.  A  definite  mixture 
of  air  and  steam  is  blown  upwards  through  the  fuel  bed, 
either  by  a  steam  injector  or  by  a  fan  or  blower,  the  steam 
in  the  latter  case  being  introduced  either  directly  or  by 
passage  of  the  air  through  or  over  water  heated  to  the 
appropriate  temperature.  It  is  important  to  have  a  thorough 
knowledge  and  control  of  the  steam/air  ratio  at  all  times. 

Uniformity  of  the  blast  throughout  the  fuel  bed  is  all- 
important.  The  method  of  effecting  such  distribution  varies 
from  the  practice  of  using  as  tuyere  a  perforated  hut-shaped 
box  as  in  the  Duff  producer,  or  some  other  distributing 
device  at  the  bottom  of  the  generator,  to  the  method  most 
usually  adopted  of  enclosing  the  grate  in  an  airtight  casing 
to  which  the  blast  is  supplied.  The  grate  may  consist  either 
of  horizontal  fire-bars  or  of  circumferentially  disposed  bars 
inclined  at  about  45°  C.  to  the  vertical,  e.g.  as  in  the  Mond 


336  INDUSTRIAL  GASES 

and  Alma  producers.  The  area  of  the  grate  should  be 
approximately  equal  to  that  of  the  generator  section,  other- 
wise excessive  local  heating  and  clinkering  are  liable  to 
occur. 

A  point  of  great  importance  is  the  provision  of  suitable 
means  for  effecting  the  removal  of  the  ashes.  In  most 
types,  e.g.  the  Mond  producer,  the  casing  enclosing  the  grate 
is  open  below  and  is  sealed  by  water,  this  procedure  allowing 
of  the  removal  of  the  ashes  through  the  water  without  inter- 
ruption of  the  working.  Considerable  trouble  is  caused  by 
the  production  of  clinker,  which  is  difficult  to  remove  and 
offers  resistance  to  the  passage  of  the  blast,  and  by  the 
adherence  of  such  clinker  to  the  lining  in  the  zone  of  highest 
temperature,  i.e.  just  above  the  grate ;  consequently, 
in  some  plants,  e.g.  the  Kerpely,  the  walls  of  the  producer 
corresponding  to  the  lower  third  of  the  fuel  bed  are  water- 
jacketed.  This  procedure  has  also  the  effect  of  furthering 
ammonia  recovery  (vide  infra).  In  this  generator  the 
ashes  are  automatically  removed  by  means  of  a  special 
revolving  grate.  This  consists  of  a  perforated  eccentrically 
constructed  conical  furnace  bottom  mounted  in  a  circular 
trough  which  revolves  once  in  2-4  hours,  a  water-sealed 
joint  being  made  with  the  furnace  casing.  The  eccentric 
construction  has  the  effect  of  breaking  up  and  ejecting 
clinker.  Air  may  be  admitted  either  uniformly  over  the 
whole  of  the  conical  surface  or  preferentially  at  the 
centre  or  the  periphery.  In  order  to  protect  the  fire-bars  of 
producers  from  the  high  temperatures  attending  the  first 
action  of  the  air  on  the  fuel  and  to  minimize  loss  of  heat, 
a  fairly  deep  layer  of  ashes  rests  on  the  actual  grate,  but  for 
small  producers  this  procedure  is  not  always  followed. 
Arrangements  are  provided  in  some  types  of  producer  for 
automatically  clearing  the  fire-bars.  According  to  recent 
tests  by  Bunte  and  Terres  (/.  Gasbeleucht.,  61,  (1918),  433, 
445)  with  Kerpely-Marischka  producers,  the  thermal 
efficiency  was  8i'6  %,  while  the  loss  by  radiation  was  equiva- 
lent to  about  2  %  of  the  total  heat,  all  the  steam  being 
generated  by  the  water-j  acket  boiler. 


GASEOUS  FUELS  337 

A  high  rate  of  gasification  is  important  and  depends  on 
adequate  grate  area  and  on  the  avoidance  of  choking  and 
channelling  in  the  fuel  bed.  Such  troubles  may  be  caused 
by  the  fuel  being  too  small  or  having  a  tendency  to  cake. 
In  the  Kerpely  producer  referred  to  above,  four  special  J- 
shaped  stirrers  are  arranged  in  the  upper  part  of  the  fuel  bed 
and  slowly  revolve  about  their  axes  and  also  as  a  whole  round 
the  furnace.  This  type  of  producer,  which  is  used  chiefly 
on  the  Continent,  is  well  suited  for  the  gasification  of  very 
low  grade  fuels,  in  treating  which  blast  pressures  up  to  30 
in.  of  water  are  employed.  It  was  shown  in  Bone  and 
Wheeler's  experiments  (p.  329  et  seq.)  that  a  shallow  fuel  bed, 
of  3 J  ft.  depth,  gave  a  carbon  dioxide  content  approximately 
equal  to  that  obtained  with  the  7-ft.  bed,  and  in  addition 
gave  a  higher  rate  of  gasification  owing  to  the  decreased 
resistance  of  passage.  Further,  less  trouble  with  clinker 
and  adherence  of  same  to  the  producer  are  experienced. 
Many  producers  are  operated  with  beds  of  about  this  depth, 
while  in  others  depths  up  to  about  7  ft.  are  used. 

As  regards  the  influence  of  the  size  of  the  fuel  on  the 
reaction  velocity,  the  active  surface  exposed  will  be  roughly 
inversely  proportional  to  the  size  of  the  lumps  of  fuel.  Dry- 
ness  of  the  steam  is  important,  and  in  many  producers  a 
pre-heating  is  effected,  either  by  definite  heat-interchange 
with  the  hot  gases  leaving  the  producer,  or  by  passage  through 
the  annular  space  surrounding  the  lower  part  of  the  producer. 
The  blast  pressure  in  pressure  producers  is  usually  about 
3-6  in.  of  water,  but  may  be  as  high  as  20  in.  or  even 
higher.  Some  producers  have  a  bell  projecting  into  the 
upper  part  of  the  interior  in  order  to  minimize  tar  production 
by  compelling  the  products  of  distillation  of  the  upper  layers 
of  fuel  to  pass  through  the  highly  heated  zone  ;  the  efficacy 
is,  however,  doubtful. 

Useful  data  relating  to  the  operation  of  various  makes 
of  producers  are  given  by  Mills  (Trans.  Inst.  Mining 
Engineers,  (1915),  723). 

Ammonia  Recovery  and  Cleaning  of  Semi-Water 
Gas. — The  extent  to  which  the  purification  of  semi-water  gas 
A.  22 


338  INDUSTRIAL   GASES 

from  suspended  matter  is  carried,  is  necessarily  dependent 
on  the  purpose  to  which  the  gas  is  to  be  put.  If  to  be  used 
directly  in  furnaces,  the  5  %  or  so  of  the  total  carbon  going 
to  tar  is  with  advantage  left  in  the  gases  both  on  account  of  its 
calorific  value  and  to  avoid  loss  of  the  sensible  heat  of  the 
gases,  the  temperature  of  which  is  usually  about  500-600°  C. 
on  leaving  the  generator.  When  such  purification  of  the 
gas  is  necessary,  principally  in  the  production  of  gas  for 
power  purposes,  the  removal  of  the  tar,  except  in  the  case  of 
relatively  small  suction  plants,  is  usually  performed  in  con- 
junction with  ammonia  recovery  and  it  will  be  advantageous 
to  consider  the  two  operations  together.  In  the  first  place, 
when  ammonia  recovery  is  to  be  effected  it  is  necessary  to 
keep  down  the  temperature  in  the  producer  (cf.  Table  24, 
p.  216,  relating  to  the  concentrations  of  ammonia  existing 
in  equilibrium  with  nitrogen  and  hydrogen  at  high  tempera- 
tures), and  this  is  usually  accomplished  (i)  by  the  use  of  a 
large  proportion  of  steam  in  the  blast,  (2)  by  cooling  the  walls 
of  the  generator. 

The  influence  of  the  steam/air  ratio  is  well  shown  by  the 
experiments  of  Bone  and  Wheeler  (cf.  Table  35),  in  which 
the  ammonia  recovered  is  seen  to  rise  from  39  to  72  Ibs. 
ammonium  sulphate  per  ton  coal  according  as  the  saturation 
temperature  is  changed  from  60°  C.  to  80°  C.,  equivalent  to 
a  variation  of  the  weight  of  steam  per  Ib.  fuel  from  0*45  to 
1-55  Ibs.  This  advantage  is,  of  course,  gained  at  the  expense 
of  a  considerable  increase  in  the  percentage  of  carbon  dioxide 
and  of  a  greater  loss  of  heat  in  the  gases. 

In  the  Moore  producer  for  ammonia  recovery  (cf. 
Engineering,  (1915),  326),  by  water-jacketing  the  walls  of 
the  producer  of  which  the  upper  part  is  air  cooled,  the  water- 
jacket  acting  as  a  steam  boiler,  it  is  claimed  that  effective 
ammonia  recovery  can  be  secured  with  the  use  of  only  about 
i  Ib.  steam/lb.  fuel,  half  of  which  steam  is  generated  by  the 
annular  boiler,  as  compared  with  ii  to  2  Ibs.  in  usual  Mond 
practice.  The  gas  produced  has  the  percentage  com- 
position— 


GASEOUS  FUELS  339 

Hydrogen      . .  .  .  .  .  26-0 

Carbon  monoxide  . .  . .  18*4 

Carbon  dioxide  . .  . .  ir6 

Methane        . .  . .  .  ,  2'2 

Nitrogen        . .  . .  . .  40*0 

Water  vapour  . .  . .  1*8 

100*0 

and  leaves  the  generator  at  a  temperature  of  about  200°  C. 

Mond  Process.— The  first  attempt  at  gasification  of  coal 
with  ammonia  recovery  and  the  production  of  a  cheap  fuel 
gas  was  due  to  Mond,  who  erected  an  experimental  plant  in  the 
Midlands  in  1879  >  the  success  of  this  experiment  led  to  the 
construction  of  the  present  large  plant.    In  the  Mond  process, 
the  air-steam  blast  is  led  into  an  annular  casing  surrounding 
the  lower  part  of  the  producer  and  serving  to  some  extent  as 
a  pre-heater.     The  grate  has  inclined " fire-bars  and  is  water- 
sealed.     In  view  of  the  high  steam  content — about  2  Ibs./lb. 
coal,  equivalent  to  saturation  at  about  85°  C. — only  ^  of 
which  is  decomposed,  it  is  necessary  to  arrange  for  the 
eificient  recuperation  of  the  sensible  heat  carried  away  from 
the  producer  thereby.     The  gases,  together  with  the  excess 
steam,  leave  the  generator  at  a  temperature  in  the  region 
of  500-600°  C.  and  pass  first  to  a  heat-interchanger,  being 
cooled   to  300-400°  C.  by  the  counter-current  flow  of    the 
air-steam  blast  entering  the  generator.     Further  reduction 
is  effected  in  a  water  washer  fitted  with  agitators  where  also 
the  tar  is  mostly  removed,  and  ammonia  is  abstracted  by 
passage  up  a  tower  down  which  a  solution  containing  about 
36-38  %    ammonium    sulphate    and    some  2*5  %   of    free 
sulphuric  acid  is  flowing.     The  gases  emerge  at  a  temperature 
of  about  80°  C.,  and  are  cooled  in  a  further  tower  with  water 
which  is  subsequently  utilized  for  the  saturation  of  the  blast 
at  about  75°  C.  in  a  third  tower.     In  the  recent  types  of 
plant  built  by  the  Power  Gas  Corporation,  the  towers  are 
sometimes  replaced  by  horizontal  chambers.     By  rneans  of 
a  further  quantity  of  steam  the  saturation  is  raised  to  85°  C. 
and  the  wet  blast  enters  the  generator  after  traversing  the 


340  INDUSTRIAL   GASES 

heat-interchanger  referred  to  above,  whereby  its  tempera- 
ture is  raised  to  about  250°  C. 

With  bituminous  coal  containing  i*2-i*6  %  nitrogen  a 
recovery  of  about  80-90  Ibs.  ammonium  sulphate/ton  coal 
can  be  realized  on  the  Mond  system  with  a  yield  of  gas 
equivalent  to  about  160,000  ft.3  at  15°  C.  per  ton  coal  (14-0 
Ibs.  coal/iooo  ft.3  at  15°  C.)  of  calorific  value  about  87  gross, 
78  net  C.H.U./ftA 

A  representative  analysis  of  semi- water  gas  with  ammonia 
recovery  is  given  in  Table  29.  It  will  be  noted  that  the 
hydrogen  and  carbon  dioxide  are  high  and  the  carbon  mon- 
oxide low.  The  large  plant  operating  at  Dudley  Port  on 
the  Mond  system  produces  gas  of  net  calorific  power  about 
75  C.H.U./ft.3  at  15°  C.,  which  is  distributed  over  an  area  of 
about  1 20  square  miles,  the  cost  (pre-war)  being  about 
if^./iooo  ft.3.  The  chief  drawbacks  of  the  Mond  process  are 
the  high  percentage  of  inert  matter — nitrogen,  carbon 
dioxide — present  in  the  gas,  and  the  large  capital  outlay 
which  renders  a  plant  of  turnover  less  than  about  150-200 
tons  coal/week  unprofitable.  The  latter  objection,  it  is 
claimed,  has  been  met  by  plants  of  later  date,  e.g.  the  Crossley 
plant,  which  claims  to  work  profitably  with  a  weekly  fuel 
consumption  of  about  TOO  tons,  the  lyymn  plant  (Engineering, 
(1915),  624),  etc.  In  the  Crossley  plant  the  general  procedure 
is  similar  to  that  followed  in  the  Mond  process,  the  main 
difference  consisting  in  the  replacement  of  the  towers  by  a 
series  of  chambers  fitted  with  revolving  paddles.  In  these 
chambers  cooling  and  ammonia  absorption  are  effected, 
the  hot  liquor — at  about  80°  C. — being  circulated  to  saturate 
the  incoming  air — at  about  60°  C. — and  returned  at  about 
40°  C.,  slightly  acidified  with  sulphuric  acid,  to  the  absorbing 
chamber,  a  portion  being  periodically  removed  for  evaporation. 
It  is  possible  to  gasify  successfully  even  such  fuels  as  lignite, 
peat,  etc.,  containing  60  %  moisture,  by  the  Mond  process. 

Use  of  Semi-Water  Gas  for  Furnace  Operations 

The  most  important  application  of  semi-water  gas  for 
furnace  work  is  in  the  Siemens  open-hearth  furnace  for  steel 


GASEOUS  FUELS  341 

melting.  The  hot  gases  leaving  the  generator  at  500- 
600°  C.  and  containing  a  considerable  amount  of  tar,  are  led 
to  the  regenerator  which  consists  of  chambers  filled  with 
chequer-work.  The  chambers  are  traversed  alternately 
by  the  products  of  combustion  in  the  furnace  and  by  the 
incoming  gas  and  air,  the  two  latter  entering  through 
separate  chambers,  of  course.  The  temperature  in  the 
regenerator  is  in  the  neighbourhood  of  1100-1200°  C.  and 
the  steel  is  heated  to  about  1600°  C. 

According  to  Hadfield  (Soc.  Brit.  Gas  Industries,  Presi- 
dential Address,  April  i8th,  1918),  the  volume  of  air  used 
in  the  practical  operation  of  such  a  furnace  is  found  to  be 
from  iJ-2  times  that  demanded  by  theory  ;  the  volume 
of  semi-water  gas  required  for  the  melting  of  i  ton  of  steel 
in  the  open-hearth  furnace  is  stated  to  be  about  48,500  ft.3 
or  2i'6  ft.3/lb.,  equivalent  to  a  thermal  efficiency  of  the  order 
of  17  %,  taking  the  net  calorific  value  of  semi- water  gas  as 
85  C.H.U./ft.3 

Stress  has  already  been  laid  on  the  importance  of  avoiding 
excess  hydrogen  and  of  maintaining  a  high  carbon  monoxide 
content ;  12-14  %  hydrogen  is  considered  the  maximum 
which  is  desirable  (Bone),  both  on  account  of  the  radiation 
from  the  flame  and  the  danger  of  back-firing. 

The  Production  of  Power  by  the  Combustion  of 
Semi-Water  Gas  in  Gas  Engines 

Some  reference  has  already  been  made  to  the  advantages 
of  internal  combustion  engines  for  the  generation  of  power 
especially  for  relatively  small  units.  Since,  as  we  shall  see 
later,  the  overall  net  efficiency,  i.e.  inclusive  of  the  steam 
for  the  generator  and  the  power  for  operating  the  blowers, 
scrubbers,  etc.,  of  a  gas  producer  may  be  safely  taken  at 
75  %,  then  for  7000  C.H.U./lb.  coal,  we  have  5250  C.H.U. 
in  the  gas.  Now  the  efficiency  of  a  modern  gas  engine  is 
about  27  % — referred  to  B.H.P. — being  practically  indepen- 
dent of  size  over  say  100  H.P.  The  useful  power  production, 
therefore,  will  be  equivalent  to  5250  X  0*27  C.H.U.  =  1417 
C.H.U.,  and  since  i  B.H.P.H.  =  1415  C.H.U.,  to 


342  INDUSTRIAL  GASES 

1417/1415  B.H.P.H.  =  roo  B.H.P.H./lb.  coal ;  the  overall 
efficiency  being  1417/7000  =  0*202.  With  100  %  efficiency, 
i  Ib.  of  coal  would  produce  about  7000/1415  =4*95  B.H.P.H. 

Using  steam  power,  on  the  other  hand,  with  a  boiler 
efficiency  of  say  75  %,  representative  of  good  practice,  and  an 
engine  efficiency  of  say  15  %,  a  value  only  obtained  with 
large  units,  we  have  a  final  power  production  equivalent  to 
7000  x  075  x  0*15  C.H.U./lb.  coal  =  787  C.H.U.  =787/1415 
B.H.P.H.  =  0-56  B.H.P.H.  per  Ib.  coal,  or  i  B.H.P.H.  for 
1*8  Ibs.  coal,  the  overall  efficiency  being  787/7000  =  0-112. 

It  should  be  pointed  out  that  the  above  values  apply 
only  to  very  large  units.  In  the  case  of  gas  engines,  however, 
the  figures  are  only  slightly  lower  for  plants  of  say  100  H.P. 
or  even  smaller,  while  the  efficiency  for  a  similar  steam  plant 
may  be  of  the  order  of  half.  On  the  other  hand,  the  very 
large  modern  turbine  sets  now  in  vogue  for  electrical  power 
generation  give  an  almost  equivalent  efficiency,  e.g.  the 
35,000  H.P.  Parsons  turbine  plant  recently  installed  at  the 
Fisk  Street  power  station,  Chicago,  uses  steam  equivalent, 
if  we  take  a  boiler  efficiency  of  75  %,  to  about  i  Ib.  coal  per 
B.H.P.H.  ;  this  represents  an  efficiency  of  about  27  %  in 
the  steam  turbine.  Another  point  in  favour  of  steam  plant 
for  large  power  units  is  the  lower  maintenance  cost. 

An  interesting  possibility  of  increasing  the  overall  thermal 
efficiency  of  the  power  production  lies  in  the  utilization  of 
the  sensible  heat  of  the  exhaust  gases  of  a  gas  engine,  e.g. 
by  passage  through  Bone-Court  or  other  boilers  and  utilizing 
the  steam  thus  produced  in  the  usual  way.  With  such  a 
procedure,  from  the  40  %  or  so  of  the  heat  units  of  the  gas 
which  leave  in  the  exhaust  (=  40  X  075  =30%  of  the 
original  calorific  value  of  the  fuel)  taking  a  boiler  efficiency 
of  075  and  an  engine  efficiency  of  0*15,  we  have  another 
30  X  075  X  0-15  %  =  3-4  %  to  add  to  the  overall  thermal 
efficiency.  An  alternative  scheme  is  to  generate  steam  by 
direct  combustion  of  producer  gas,  produced  from  very  low 
grade  fuel,  under  the  boilers.  The  foregoing  remarks  as  to 
efficiency  relate  also  to  gas  engines  working  on  blast  furnace 
gas  (vide  infra). 


GASEOUS  FUELS  343 

Plants  for  Power  Generation. — For  this  purpose  we 
have  a  choice  of  pressure  plants,  either  with  or  without 
ammonia  recovery,  and  suction  plants,  and  of  using  as 
fuel  anthracite,  coke,  bituminous  coal,  lignite,  etc.  The 
respective  economics  of  the  alternatives  are  somewhat 
complex  but  it  will  suffice  to  give  a  few  generalizations. 
Suction  plants  are  used  up  to  sizes  of  the  order  of  500  H.P. 
on  account  of  their  greater  thermal  efficiency  and  are  usually 
operated  with  anthracite  or  gas  coke  for  relatively  small 
plants,  say  250  H.P.,  to  avoid  the  troublesome  cleansing 
treatment,  with  its  attendant  loss  of  pressure  on  the  engine 
suction  pipe,  necessary  with  bituminous  fuel.  When, 
however,  very  large  plants  are  required,  of  1000-2000  H.P., 
the  importance  of  ammonia  recovery  and  of  the  utilization 
of  low  grade  fuel  outweighs  the  cheapness  and  convenience 
of  the  suction  plant. 

In  all  cases,  it  is  important  to  remove  the  tar  very  tho- 
roughly and  to  cool  down  the  gases  practically  to  atmospheric 
temperature  before  admission  to  the  engine.  Using  anthra- 
cite the  problem  is  comparatively  simple  and  scrubbing  in 
towers  containing  coke  moistened  with  water  is  often  sufficient, 
though  this  is  sometimes  preceded  by  passage  through  atmo- 
spheric coolers,  and,  when  using  coke  or  inferior  anthracite, 
further  treatment  in  a  dry  sawdust  scrubber  may  be  required. 
With  bituminous  coal  it  is  necessary  (i)  to  take  steps  to 
minimize  the  production  of  tar  in  the  generator,  or  (2)  to  use  a 
centrifugal  or  static  extractor  after  the  scrubbers.  Method 
(i),  which  is  not  so  much  in  favour  as  (2),  depends  on  the 
passage  of  the  gases  arising  from  the  distillation  of  the  fuel 
in  the  upper  layers  of  the  generator,  through  the  zone  of  high 
temperature,  e.g.  in  the  Dowson  plant  a  supply  of  secondary 
air  is  taken  in  at  the  top  of  the  producer  and  the  gases  are 
withdrawn  at  about  the  centre  of  the  fuel  bed  ;  in  the  Duff- 
Whitfield  producer  the  tarry  vapours  from  the  upper  part  of 
the  producer  are  drawn  away  by  steam  injectors  and  forced 
upwards  through  the  lower,  high  temperature  zone  of  the 
fuel  bed,  the  gases  leaving  at  about  the  centre  of  the  bed. 
The  "  cracking "  of  tar  proceeds  very  slowly,  however, 


344  INDUSTRIAL   GASES 

and  for  this  reason  method  (2)  is  generally  considered 
preferable.  (2)  Static  tar  fog  separators  usually  depend  on 
the  principle  of  bubbling  the  gas  in  fairly  fine  streams  through 
water,  as  in  the  Livesey  apparatus,  the  gas  passing  through 
narrow  orifices  or  slits ;  or  in  subjecting  to  abrupt  changes 
of  direction  by  suitable  baffles  as,  e.g.,  in  the  Pelouze  and 
Audouin  separator.  Surfaces  covered  with  a  film  of  tar  are 
much  more  efficacious  in  the  removal  of  suspended  tar  than 
when  moistened  with  water.  In  the  Smith  Gas  Power 
Corporation's  separator,  the  gas  is  filtered  through  a  glass- 
wool  mat,  a  pressure  drop  of  from  2-4  lbs./in.2  being  neces- 
sary. The  dynamic  types  usually  rely  on  centrifugal 
force.  Thus  in  the  Crossley  centrifugal  fan  extractor,  the 
gas,  together  with  water  passes  over  the  periphery  from  one 
side  of  a  rapidly  rotating  disc  fitted  with  vanes,  to  the  axis 
on  the  other  side.  Mention  may  also  be  made  of  the  method 
of  electrostatic  separation  which  has  been  found  to  effect  a 
satisfactory  removal  of  tar  (cf.  White,  Hacker  and  Steere, 
/.  Gas  Lighting,  119,  (1912),  825  ;  White,  Rowley  and  Wirth, 
/.  Soc.  Chem.  Ind.,  (1914),  1000  ;  Steere,  Ib.,  (1914),  1145  ; 
(1915),  415).  In  Gas  /.  (1918),  August  I3th,  it  is  stated  that 
coal  gas  can  be  treated  with  a  power  expenditure  of  0*0008 
K.W.H./iooo  ft.3.  In  all  scrubbing  appliances  for  suction 
plants  it  is  important  to  make  the  loss  of  head  as  small  as 
possible  as  pointed  out  above,  hence  sawdust  filters,  etc.,  are 
perferably  made  of  disc  form  rather  than  long  and  narrow  ; 
sometimes  a  booster  fan  is  inserted  before  the  engine. 

Suction  Plants. — The  principle  of  drawing  the  gas  through 
the  generator  by  the  suction  of  the  engine  (originally  sug- 
gested by  Benier  (1896),  the  technical  development  of  the 
modern  gas  engine  operating  at  high  compression  on  gases 
of  low  calorific  value  being  mainly  due  to  the  pioneering 
work  of  Dowson)  has  led  to  the  evolution  of  a  very  compact 
and  serviceable  type  of  power  plant  which  now  plays  an 
important  role  in  power  generation  and  is  destined  to  have 
even  greater  importance  in  the  future. 

Suction  plants  have  an  advantage  in  the  reduction  of 
risk  of  carbon  monoxide  poisoning  owing  to  the  prevailing 


GASEOUS  FUELS  345 

negative  pressure.  Gas  from  pressure  producers  lias  usually 
a  slightly  higher  calorific  value  than  that  from  suction  plants, 
(10-20  %)  ;  further,  the  pressure  drop  with  the  latter,  of 
the  order  of  6  in.  of  water,  renders  the  power  development 
with  a  given  engine  somewhat  smaller.  In  the  smaller 
suction  plants  the  steam  is  often  generated  in  an  annular 
boiler  disposed  as  a  jacket  to  the  generator,  loss  of  heat  by 
radiation  being  thus  minimized  ;  in  other  types  the  sensible 
heat  of  the  gases  is  utilized  in  a  multitubular  vaporizer ;  flash 
vaporizers  are  also  employed.  The  result  is  to  make  the 
overall  thermal  efficiency  somewhat  greater  than  for  pressure 
producers  with  independent  boilers.  The  sensible  heat 
of  the  exhaust  gases  may  be  employed  for  steam  raising  as 
e.g.  in  the  Smith  (Ohio)  plant. 

A  point  in  connection  with  suction  plants  requiring  some 
attention  is  the  lag  in  the  response  of  the  generator  to  a 
sudden  variation  of  load  on  the  engine  ;  if  the  load  has  been 
light  for  some  time  the  temperature  in  the  fuel  bed  will  fall 
and,  on  a  sudden  rise  in  the  gas  requirements,  only  a  poor  gas 
will  be  available  for  a  period.  This  difficulty  is  minimized 
by  the  use  of  a  gas-holder  and  by  allowing  the  gas  to  go  to 
waste  during  such  "  heating  up  "  periods,  or  alternatively, 
by  making  some  gas  to  waste  during  the  light  load  period. 
In  some  cases  automatic  steam  regulation  operated  by  the 
gas-holder  is  provided. 

On  starting  up  a  suction  generator  the  procedure  is  to 
"  blow  up  "  the  producer  with  an  auxiliary  fan,  the  gases 
passing  to  the  flue  until  of  sufficiently  good  quality,  as  judged 
from  the  flame  at  a  test  cock.  The  depth  of  fuel  bed  varies 
from  2-3  ft.  according  to  the  size  of  the  plant.  According 
to  Burt,  the  volume  of  the  generator  varies  from  0-12  to 
0-18  ft.3/B.H.P.  as  the  capacity  increases  from  20-100 
B.H.P. ;  the  grate  area  is  usually  some  J  that  of  the  cross- 
section.  Owing  to  the  necessity  for  continuous  working  over 
long  periods,  ample  capacity  must  be  allowed  for  the  accumu- 
lation of  the  large  lumps  of  clinker  ;  charging  of  fuel  is 
usually  performed  only  at  intervals  of  say  6-12  hours, 
adequate  fuel  capacity  being  provided.  The  arrangement 


346  INDUSTRIAL   GASES 

of  a  layer  of  ashes  above  the  fire-bars  is  usual  in  suction 
producers.  The  rate  of  gasification  is  of  the  order  of  15-30 
lbs./ft.2  depending  on  the  fuel  burnt.  Special  types  of 
generator  are  used  for  small,  waste  fuels,  etc.,  as,  e.g.  the 
Ruston  plants  for  the  gasification  of  sawdust,  straw  and  the 
like.  Even  untreated  seaweed  may  be  used.  Owing  to  the 
method  of  generating  the  steam  in  suction  plants  the  satura- 
tion temperature  is  liable  to  vary  considerably  both  from 
time  to  time  and  from  one  plant  to  another ;  less  variation  is 
experienced  with  flash  vaporizers  with  automatic  regulation 
of  the  water  feed.  The  net  thermal  efficiency,  allowing  for 
the  power  of  the  suction  and  including  the  generation  of  the 
steam,  is  usually  75  %  to  80  %.  Fuel  consumption  varies 
from  about  12  Ibs./iooo  ft.3  of  gas  at  15°  C.  with  anthracite 
to  about  1 6  Ibs.  with  bituminous  coal. 

Use  of  Suction  Gas  in  Internal  Combustion  Engines. 
— Reference  to  Table  29  will  indicate  that  although  consider- 
able differences  exist  between  the  calorific  values  of  the  various 
fuel  gases,  e.g.  that  of  coal  gas  is  some  4  times  that  of  suction 
gas,  there  is  little  difference  between  those  of  the  theoretical 
mixtures  with  the  necessary  air  for  combustion  except  in 
the  case  of  semi-water  gas,  air  producer  gas,  and  blast  furnace 
gas,  which  have  slightly  lower  values.  Further,  in  practi- 
cally all  cases  gaseous  fuels  are  used  with  a  sufficient  excess 
of  air  (a  relatively  small  excess  being  required  for  semi- 
water  gas,  blast  furnace  gas,  etc.),  to  reduce  the  calorific 
value  of  the  mixture  to  about  25-30  C.H.U./ft.3,  it  being 
specially  necessary  to  keep  down  the  calorific  value  in  very 
large  engines. 

The  permissible  degrees  of  compression  without  causing 
pre-ignition  are  given  by  lyucke  as  : — 

Gas.  Coal  gas.      Semi-water  Blast  furnace 

Compression  (lbs./in.2  > 

excess  pressure)       )    °°  J35  J55 

Trouble  experienced  with  pre-ignition  is  usually  attributed 
to  the  presence  of  excess  hydrogen,  but  considerable  doubt 
appears  to  exist  on  the  point ;  apparently  mixtures  as  rich 


GASEOUS   FUELS  347 

as  40  %  hydrogen  can  be  worked  successfully  if  'the  com- 
pression be  not  too  great  (cf.  discussion  on  paper  by  Bone 
and  Wheeler,  p.  329).  There  is  some  evidence  to  suggest  that 
pre-ignition  may  be  caused  by  the  minor  constituents  of  semi- 
water  gas,  e.g.  to  traces  of  carbon  disulphide,  acetylene,  etc. 

An  interesting  discussion  of  the  above  mentioned  points 
relating  to  gas  engines  will  be  found  in  a  paper  by  Tookey 
(/.  Soc.  Chem.  Ind.,  (1917),  309).  As  regards  the  volume  of 
gas  required  for  the  production  of  i  B.H.P.H.  =  1415 
C.H.U.,  taking  the  efficiency  of  the  engine  at  27  %,  the  heat 
units  required  in  the  gas 


0*27 

and,    taking    the    net    calorific    value    of    suction    gas    as 
70  C.H.U./ft.3  at  15°  C.,  we  see  that  the  requirements  are 


5250 


ft.3  =  75  ft.3  at  15°  C. 


70 

This  applies  to  a  fairly  large  plant. 

According  to  Brame,  coal  gas  becomes  less  economical 
than  suction  gas  when  the  plant  exceeds  about  50  H.P. 

We  have  seen  above  that  the  production  of  B.H.P.H. 
should  require  the  gasification  of  about  i  Ib.  of  coal,  and  this 
amount  is  closely  approached  when  anthracite  is  used  even 
in  small  plants  and  is  improved  upon  in  many. 

Coal  Gas  as  a  Fuel 

It  is  not  proposed  to  enter  into  a  description  of  the  manu- 
facture of  coal  gas,  an  average  composition  of  which  may  be 
found  in  Table  29.  The  composition  varies  to  some  extent 
with  the  temperature  of  carbonization  and  with  the  size  of 
the  retort  and  is  somewhat  different  with  the  modern  con- 
tinuous system.  The  effect  of  high  carbonization  tempera- 
tures is  to  raise  the  percentage  of  hydrogen  and  to  lower 
that  of  methane.  The  coal  required  per  1000  ft.3  of  gas  at 
15°  C.  is  usually  of  the  order  of  17-20  Ibs.  The  former 
legal  standard  was  one  of  illuminating  power,  namely  16  candle 
power  per  ft.3,  but  with  the  advent  of  the  incandescent 
mantle  together  with  the  increasing  use  of  coal  gas  for  power 


34^  INDUSTRIAL   GASES 

and  heating  purposes  this  standard  became  of  secondary 
importance  and  in  some  districts  has  been  partly  replaced 
by  one  of  calorific  value,  namely  276  C.H.U./ftA 

It  should  be  remembered  that  nearly  all  town  gas  contains 
a  considerable  proportion  of  carburetted  water  gas  or  even 
of  blue  water  gas ;  the  calorific  value  of  carburetted  water 
gas  is,  however,  not  greatly  different  from  that  of  coal  gas. 

The  sulphur  content  of  coal  gas  is  important  in  connection 
with  its  domestic  and  industrial  uses,  e.g.  in  metal  melting, 
annealing,  etc.,  at  least  in  such  cases  as  the  metal  is  exposed 
to  the  products  of  combustion.  The  initial  high  content 
(according  to  Meade  the  H2S  present  in  crude  coal  gas  is  of 
the  order  of  500-800  grains/ioo  ft.3  =  0-8-1-3  %  by 
volume,  in  addition  to  some  35-50  grains/ioo  ft.3  of  other 
sulphur  compounds)  is  reduced  by  methods  described  else- 
where to  a  value  of  the  order  of  35-50  grains/ioo  ft.3,  the 
residue  being  mostly  carbon  disulphide. 

General.— Applications  of  Coal  Gas.— For  small 
plants,  coal  gas  has  many  advantages  over  the  cheaper 
producer  gas  on  account  of  the  absence  of  any  overhead  or 
standby  costs  in  the  way  of  generators,  gas-holders,  and  fuel 
storage,  and  in  uniformity  as  regards  quality,  pressure,  etc. 

Furnace  Operations. — Of  late  years,  and  especially 
during  the  war,  gas  firing  has  come  into  extensive  use  for 
metal  melting,  annealing,  and  reheating  operations.  Much 
useful  information  on  the  subject  of  gas  firing  of  crucibles 
for  the  melting  of  non-ferrous  alloys  may  be  obtained  from 
the  Annual  Reports  of  the  Royal  Mint,  the  results  of  the 
working  being  summarized  by  Hocking  in  Trans.  Inst. 
Metals,  (1917),  ii.,  149.  The  following  table,  compiled  from 
Hocking's  paper,  indicates  the  general  result  of  changing 
the  melting  system  from  one  using  coke  to  a  gas  fired  system : — 


Fuel  used     Cost  of  fuel  per  ton  metal 
per  Ib.           (coke,  3875.  per  ton) 
metal.        (gas,  ao'ad.  per  1000  ft.  3). 

Cost  in  crucibles 
per  ton  metal. 

Coke  melting  (1905-1909) 
Gas  melting  (1911-1916) 

0-55  Ibs.          21-3    shillings 
5-45  ft3.   :       20-58  shillings 

39-  8  shillings 
26-8  shillings 

GASEOUS  FUELS  349 

If  the  net  calorific  value  of  the  coke  be  taken  as  8000 
C.H.U./lb.  and  that  of  the  gas  be  taken  as  280  C.H.U./ft.*,  the 
heat  units  expended  per  Ib.  metal  are  (i)  coke,  4400  C.H.U. ; 
(2)  gas,  1526  C.H.U. 

A  reduction  in  wages  from  157  to  10*8  shillings  per  ton 
metal  was  also  recorded  for  the  years  1909  and  1913  respec- 
tively with  coke  and  gas  firing.  The  output  per  furnace  was 
increased  to  from  190  %  to  260  %  of  that  realized  with  coke 
according  to  the  alloy  melted.  The  gain  in  speed  is,  of  course, 
most  pronounced  with  the  first  heat. 

Somewhat  similar  conclusions  are  arrived  at  by  Brook, 
using  a  Brayshaw  furnace  (Trans.  Inst.  Metals,  (1917),  ii., 
171).  According  to  Forster  (/.  Soc.  Chem.  Ind.,  (1917), 
1264),  the  gas  consumption  varies  from  2*4  ft.3/lb.,  equivalent 
to  some  21  %  efficiency,  in  melting  60/40  brass  ingots  to  8-5 
ft.3/lb.  (efficiency  some  7-8  %),  in  melting  cupro-nickel, 
using  the  ordinary  pit  type  of  furnace.  Amongst  advantages 
may  be  mentioned  the  ease  of  recovery  of  spillings  by  avoiding 
the  necessity  of  grinding  and  washing  the  ashes,  as  in  the 
case  of  the  coke-fired  furnace,  this  being  important  in  the 
melting  of  brass,  nickel  silver,  cupro-nickel,  etc.,  as  well 
as  with  precious  metals ;  further,  the  metal  from  an  acci- 
dental breakage  of  the  crucible  is  easily  recovered.  As 
regards  crucibles,  the  economy  indicated  above  can  only  be 
secured  by  the  use  of  (graphite)  crucibles  of  special  compo- 
sition ;  with  the  ordinary  variety,  as  the  author  has  experi- 
enced in  the  melting  of  nickel  silver,  etc.,  the  life  is  apt 
to  be  shortened  by  flaking,  owing  to  local  oxidation  and  to 
sudden  heating  which  do  not  occur  with  a  coke  furnace.* 

The  importance  of  the  crucible  costs,  which  a  reference 

*  It  should  be  remembered,  as  pointed  out  by  Thornton  and  Hartley, 
Trans.  Inst.  Metals,  (1917),  ii.,  306,  that  the  oxidation  of  the  graphite 
crucible  does  not  depend  simply  on  the  presence  of  less  oxygen  than  that 
corresponding  to  the  stoicheiometric  requirements  for  combustion  ;  the 
attack  on  the  carbon  will  depend  on  the  ratio  of  the  carbon  dioxide  to 
carbon  monoxide  at  any  particular  temperature,  this  ratio  in  turn  being 
conditioned  by  the  completeness  of  combustion  and  by  the  water  gas 
equilibrium.  Even  when  a  considerable  excess  of  gas  is  used  the  ratio 
CO2/CO  will  be  fairly  high,  and  a  consideration  of  the  CO/CO2/C  equili- 
brium at  the  partial  pressures  in  question  (compare  e.g.  p.  303)  will  suffice 
to  show  that  in  the  case  of  carbon,  oxidation  will  always  tend  to  occur, 


350  INDUSTRIAL  GASES 

to  the  table  will  show  to  be  greater  than  that  of  the  fuel,  is 
not  always  realized  in  the  consideration  of  non-ferrous 
melting. 

Amongst  other  advantages  of  gas  firing  may  be  mentioned 
(cf.  Greenwood  and  Hutton,  Trans.  Inst.  Metals,  (1917),  i., 
237) — (i)  the  greater  ease  of  regulating  the  heating  and  of 
maintenance  of  a  slightly  reducing  atmosphere  ;  (2)  decreased 
contamination  of  the  metal  by  sulphur;  and  (3)  greater 
ductility  of  the  alloy,  demonstrating  itself  both  by  the  ordinary 
mechanical  tests,  e.g.  greater  elongation  and  greater  endur- 
ance under  torsion,  and  also  in  the  production  of  "  difficult 
spinnings/'  a  matter  of  great  practical  importance.  There 
are,  however,  some  disadvantages,  such  as  the  noise,  increased 
zinc  losses  due  to  the  rapid  movements  of  the  gases,  etc. 

The  above  remarks  apply  particularly  to  the  usual 
practice  of  intermittent  working  in  non-ferrous  melting  ; 
for  continuous  working  on  a  fairly  large  scale,  regenerative 
producer  gas  furnaces  are  more  economical.  Thus,  Teisen 
(Trans.  Inst.  Metals,  (1917),  ii.,  257)  reports  for  a  Hermansen 
counter-current  recuperative  furnace,  a  coke  consumption  of 
O'i8  Ib./lb.  brass  melted.  In  the  design  of  melting  furnaces 
it  is  important  to  keep  down  the  combustion  space  round  the 
crucible,  the  resulting  high  gas  velocity  producing  better 
heat-interchange,  cf.  p.  45  ;  the  shape  of  the  inlet  nozzle 
is  also  important. 

Thus  far  only  melting  furnaces  have  been  considered. 
Turning  to  the  more  general  aspects  of  the  question,  gas 
furnaces  may  be  divided  into  three  general  classes :  (i)  those 
operating  with  gas  at  a  pressure  of  2  to  3  in.  of  water  and 
drawing  in  air  like  the  ordinary  Bunsen  burner ;  (2)  those 
operating  with  gas  at  a  pressure  of  2  to  3  in.  of  water  and 
air  at  i  to  3  lbs./in.2;  and  (3)  those  operating  with  gas 
at  a  comparatively  high  pressure,  e.g.  12  lbs./in.2  on 
the  Bunsen  principle.  System  (3),  which  has  been  applied 
on  an  extensive  scale  in  Birmingham,  gas  being  dis- 
tributed at  a  pressure  of  12  lbs./in.2  (cf.  Walter,  Trans. 
Inst.  Metals,  (1917),  ii.,  185),  is  more  or  less  equivalent 
to  (2).  It  has  the  advantage  of  dispensing  with  the  use 


GASEOUS  FUELS  351 

of  a  blower,  the  gas  consumption  is  greater  than  with  (2), 
but  the  lining  suffers  less.  Various  intermediate  proce- 
dures have  been  adopted,  e.g.  in  the  internally-fired  reheating 
furnaces  built  by  the  Richmond  Gas  Stove  Company;  these 
are  fed  with  air  at  a  pressure  of  a  few  inches  of  water  from  a 
fan,  the  air  not  being  mixed  with  the  gas  before  the  point 
of  combustion.  A  luminous  flame  results.  The  incoming 
air  passes  through  fireclay  tubes  in  the  furnace  bed,  in  counter- 
current  to  the  exit  gases,  and  a  high  efficiency  is  attained. 
Thus,  100  to  300  ft.3  of  coal  gas  are  required  per  cwt.  metal 
annealed,  according  to  its  thickness.  Much  more  may  be 
expected  in  the  future  from  development  of  the  principle 
of  utilizing  the  heat  of  the  products  of  combustion  for  the 
preheating  of  the  metal  and  the  air.  Efforts  in  this  direction 
have  given  thermal  efficiencies  of  the  order  of  20  %.  Pre- 
heating of  the  gas  tends  to  cause  carbon  deposits  by  cracking. 
One  of  the  best  known  furnaces  of  type  (2)  is  the  Brayshaw 
furnace.  In  many  annealing  operations,  the  maintenance 
of  a  neutral  or  reducing  atmosphere  is  of  great  importance 
in  avoiding  surface  oxidation,  decarburization,  etc.  ;  gas- 
fired  furnaces  are  eminently  suited  for  such  purposes. 
Further,  using  gas,  uniformity  of  temperature  throughout 
the  furnace  is  readily  secured. 

According  to  Hadfield  (loc.  cit.,  p.  341),  the  volume  of 
coal  gas  required  for  the  heating  of  steel  in  bulk  to  900°  C. 
is  1*23  ft.3/lb.,  equivalent  to  a  thermal  efficiency  of  32  %. 
To  give  an  idea  of  the  impetus  given  by  the  war  to  the  use 
of  coal  gas,  it  may  be  mentioned  that  the  consumption 
during  the  year  1917  at  the  works  of  Messrs.  Hadfield,  lytd., 
was  360  million  ft.3,  while  in  some  towns  the  consumption 
has  been  more  than  doubled. 

Coal  gas  is  used  extensively  in  the  heat  treatment,  forging, 
etc.,  of  tools,  including  those  of  high  speed  steel,  which  demand 
a  temperature  of  about  1300°  C.  ;  also  for  the  annealing  of 
glass  and  wire  ;  in  the  textile  industries ;  in  heating  shell- 
varnishing  stoves,  and  for  other  purposes  too  numerous  to 
mention. 

Power  Production. — Reference  has  been  made  to  the 


352  INDUSTRIAL  GASES 

relative  advantages  of  coal  gas  and  semi-water  gas  for  power 
production.  Since  the  modern  gas  engine  has  a  net  efficiency 
of  some  27  %  on  full  load,  the  volume  required  per  B.H.P.H. 
of  coal  gas  with  a  net  calorific  value  of,  say,  280  C.H.U. 
(504  B.T.U.)  per  ft.3  at  15°  C. 

=    Q  I415       ft.8  at  15°  C. 
280  x  0-27 

=  187  ft.3  at  15°  C. 

equivalent  to  5250  C.H.U. 

Other  Applications  of  Coal  Gas.— It  is  hardly  necessary 
to  dwell  here  on  the  domestic  uses  of  coal  gas.  One  may, 
however,  mention  that  the  modern  gas  fire  has  an  over- all 
efficiency  up  to  about  75  %,  some  35  to  50  %  being  directly 
radiated  into  the  room. 

During  the  war,  owing  to  the  scarcity  of  petrol,  coal  gas 
has  been  used  for  motor  traction,  in  flexible  rubber  containers 
and  also  compressed  to  some  50  atmospheres  in  steel  cylinders 
or  to  about  17  atmospheres  in  the  equivalent  of  a  large 
pneumatic  tyre.  It  is  found  that  in  practice  1000  ft.3  are 
equivalent  to  3  to  4  gallons  of  petrol. 

Coal  gas,  preferably  after  being  bubbled  through  am- 
monium hydroxide,  is  used  for  case  hardening  (cf.  /.  Gas 
Lighting,  132,  (1915),  3*2  ;  134,  (1916),  691). 

Coke-oven  Gas 

In  the  production  of  coke  for  metallurgical  purposes,  the 
early  "  beehive  "  process  which  is,  one  regrets  to  say,  still 
in  use  in  this  country,  depends  on  the  partial  combustion 
of  the  coal  (coking)  with  no  recovery  of  the  ammonia,  tar 
products,  etc.  In  the  modern  type  of  coke  oven,  carbonization 
is  effected  in  very  large  closed  retorts,  and  the  gas  evolved 
— after  treatment  for  by-product  recovery — burnt  in  part 
to  heat  the  retorts,  reasonable  efficiency  being  secured  by  the 
use  of  regenerators  or  by  passing  the  hot  products  of  com- 
bustion through  boilers.  Some  50  %  of  the  total  gas  produced 
is  required  for  the  heating  of  the  retorts  ;  the  rest  is  available. 
The  gas  has  a  composition  similar  to  that  of  coal  gas,  but  may 


GASEOUS  FUELS  353 

contain  more  nitrogen  owing  to  ingress  of  air.  Tie  weight 
of  coal  required  for  1000  ft.3,  if  no  gas  were  used  for  heating ; 
the  calorific  value  of  the  gas ;  and  the  volume  required  for 
the  production  of  one  B.H.P.H.,  are  similar  to  the  corre- 
sponding values  for  coal  gas. 

When  one  considers  that  some  20  million  tons  of  metal- 
lurgical coke  are  produced  annually  in  this  country,  the 
possible  recovery  of  gas  is  seen  to  be  of  the  order  of  13  million 
ft.3  per  hour,  equivalent  to  about  600,000  H.P.  Utilization 
for  power  purposes  is  already  in  progress  on  a  large  scale  on 
the  North-east  coast,  while  in  some  cases,  e.g.  at  I^eeds, 
Middlesbrough  and  Sheffield,  the  gas  is  piped  for  municipal 
supply.  In  such  cases  the  poorer  first  and  last  portions  of 
the  gas  are  often  collected  separately  and  used  for  the 
heating. 

Coke-oven  gas  is  often  used  in  admixture  with  blast 
furnace  gas  for  heating  steel  furnaces.  When  used  in  this 
way,  passage  through  the  regenerators  reduces  the  calorific 
value  per  unit  volume  by  some  30  %  (Simmersbach,  Stahl  u. 
Eisen,  33,  (1913),  239,  273),  and  there  are  advantages  in 
heating  the  air  alone.  By  burning  under  steam  boilers  an 
efficiency  of  60  to  70  %  can  be  obtained  with  an  evaporation 
of  about  5  lbs./ft.2/hr.  (cf.  Kershaw,  Engineer,  124,  (1917), 
28). 

Blast-furnace  Gas 

In  the  smelting  of  iron  ore  the  necessary  temperature  is 
obtained  by  the  combustion  of  (excess)  carbon  by  air,  result- 
ing in  the  production  of  very  large  volumes  of  gas  similar 
in  composition  to  air  producer  gas  except  that  more  carbon 
dioxide  is  present  (cf.  Table  29).  Originally  allowed  to 
burn  at  the  throat  of  the  furnace,  the  gas  was  used  later 
(1837)  f°r  the  pre-heating  of  the  blast  and  also  for  steam 
raising,  but  a  surplus  still  remained,  increasing  as  the  hot- 
blast  stoves  were  made  more  efficient. 

For  each  ton  of  pig  iron  produced,  about  150,000  ft.3  of 
gas  are  obtained  (according  to  Hubert),  some  60  %  being 
required  for  the  hot-blast  stoves  and  for  generating  power 
A.  23 


354  INDUSTRIAL  GASES 

for  the  blast,  etc.  Thus,  for  each  ton  of  iron  we  have  some 
60,000  ft.3  of  gas  of  net  calorific  value  about  57  C.H.U./ft.3. 
Taking  as  before  an  efficiency  of  0*27  in  the  gas  engine,  the 
power  production  per  ton  of  iron 

60,000  X  57  X  0-27 


1415 
=  652  B.H.P.H. 


B.H.P.H. 


In  consideration  of  the  enormous  quantities  of  coke 
used  for  blast  furnaces — upwards  of  10  million  tons/annum 
in  this  country — the  possible  power  development  is  obvious. 
Some  power  stations  on  these  lines  are  in  operation  on  the 
North-east  coast.  It  was  predicted  by  Hutchinson  of  the 
Skinningrove  Iron  Company,  that  the  potential  energy  of 
the  blast  furnace  gas  would  suffice  to  produce  all  the  power 
required  for  the  production  of  finished  steel  rails  from  the 
ore.  The  high  compression  of  about  155  lbs./in.2  is  used 
without  risk  of  pre-ignition. 

It  is  essential  to  remove  very  thoroughly  the  large  amount 
of  dust  in  the  gases — about  5  grams/m.3 — the  removal  being 
effected  either  dry  by  bag  filters  after  cooling  the  gas,  since 
it  leaves  the  furnace  at  about  250°  C.,  or  wet  by  a  Theissen 
fan  (Reinhardt,  Trans.  Iron  and  Steel  Inst.,  (1906),  iii.,  47), 
the  maximum  permissible  residue  being  of  the  order  of  O'oi 
gram/m.3,  or  by  a  combination  of  the  two  methods  (cf. 
also  electrostatic  dust  removal  (p.  28).  With  reference  to 
the  recovery  of  potash  from  the  blast  furnace  gases,  see  Chance, 
J.  Soc.  Chem.  Ind.,  (1918),  222T ;  Berry  and  M'Arthur, 
Ib.,  iT. 

Natural  Gas 

Natural  gas  is  evolved  from  petroleum  wells  in  prodigious 
quantities  in  the  United  States  and  Canada.  In  smaller 
amounts  it  has  been  found  also  in  Hungary,  near  Hamburg, 
and  even  in  England  (Heathfield  in  Sussex).  A  representa- 
tive composition  is  given  in  Table  29,  but  there  is  consider- 
able variation  from  well  to  well  and  also  with  the  amount 
drawn  from  a  particular  source.  Thus,  hydrogen  may  be 


GASEOUS  FUELS  355 

present  to  the  extent  of  about  20  %  while  i  %  of  carbon 
monoxide  may  be  found  in  some  samples.  Up  to  about 
i  %  of  helium  may  be  present  (cf.  pp.  131-3). 

The  gas  is  tapped  oft*  at  pressures  up  to  40  atmospheres, 
and  is  sometimes  measured  for  distribution  purposes  at 
this  pressure;  in  this  connection  the  very  considerable 
deviation  from  perfection  of  the  gas  at  high  pressure  is  of 
importance  (cf.  Burrell  and  Robertson,  U.S.  Bureau  of 
Mines,  Tech.  Paper  No.  131). 

In  the  United  States  and  Canada  the  gas  is  distributed 
over  very  large  areas  for  heating  and  lighting,  some  900,000 
million  ft.3  being  consumed  in  1917.  In  connection  with  a 
recent  cyanamide  plant  in  Hungary  some  2500  million  ft.3/ 
annum  of  natural  gas  are  being  utilized  for  power  purposes. 
If  compressed  for  distribution  in  cylinders,  some  of  the 
higher  boiling  petroleum  constituents  present  are  liquefied 
out  and  may  be  separated,  the  calorific  value  of  the  gaseous 
fraction  possibly  being  lowered  by  some  20  %  (cf.  Dykema, 
U.S.  Bureau  of  Mines,  Bull.  151).  Natural  gas  gives  a  flame 
of  high  calorific  intensity. 

There  would  appear  to  be  a  promising  field  for  research 
in  the  utilization  of  natural  gas  for  the  production  of  form- 
aldehyde— by  catalytic  oxidation  (cf.  D.R.P.  214,165) — and 
of  other  organic  compounds.  In  D.R.P.  281,084/13  Herman 
proposes  to  produce  nitric  acid  by  the  combustion  of  methane 
with  oxygen-enriched  air  under  pressure  or  by  surface 
combustion. 

An  excellent  discussion  of  the  properties  and  possible 
applications  of  methane  is  given  by  Malison0  and  Bgloff,  J. 
Phys.  Chem.,  22,  (1918),  529. 

Surface  Combustion.— The  principle  of  surface  com- 
bustion, i.e.  the  flameless  combination  of  two  gases  on  the 
incandescent  surface  of  a  solid,  was  first  suggested  by  the 
experiments  of  Davy  in  1817,  and  has  recently  been  elaborated 
by  Bone  as  a  result  of  his  researches  on  the  catalytic  combina- 
tion of  hydrogen  and  oxygen  (Phil.  Trans.,  A  206,  (1906), 
i),  and  developed  on  a  technical  basis  in  conjunction  with 
McCourt. 


356  INDUSTRIAL  GASES 

Perhaps  the  simplest  form  is  that  in  which  a  mixture 
of  gas  and  air  in  the  correct  proportions  or  with  slight  excess 
of  air,  is  forced  at  considerable  velocity  through  a  refractory 
diaphragm,  combustion  occurring  on  the  other  side  which 
becomes  highly  incandescent ;  combination  is  confined  to 
J"  or  y  below  the  surface.  It  is  necessary,  of  course,  that 
the  diaphragm  be  sufficiently  refractory  to  avoid  risk  of  fusion. 

The  advantages  of  such  an  appliance  for  heating  purposes 
are :  (i)  the  high  proportion  of  radiant  energy,  the  radiation 
from  a  solid  surface  being  proportional  to  the  fourth  power 
of  the  absolute  temperature  ;  (2)  the  fact  that  combustion 
is  effected  without  the  use  of  more  than  a  slight  excess  of 
air ;  and  (3)  that  high  temperatures  may  be  readily  obtained 
without  the  aid  of  cumbrous  regenerators.  When  applied 
to  the  heating  of  a  crucible  or  a  muffle,  a  granular  refractoty 
material  such  as  carborundum  or  fused  magnesia  is  packed 
around  and  the  gas  mixture  introduced  with  a  velocity 
sufficient  to  prevent  back-firing. 

Most  attention  has  been  paid,  however,  to  the  gas-fired 
steam  boiler,  the  efficiency  of  which  is  notoriously  low 
(usually  not  exceeding  60  %,  according  to  Bone),  owing  to 
the  relatively  small  radiation  and  the  low  rate  of  transmission 
of  heat  from  gases  to  surfaces  (cf.  p.  45).  In  the  Bone- 
Court  system  the  usual  procedure  is  to  pack  the  tubes  of  a 
multitubular  boiler — 3"  to  6"  diameter — with  a  granular 
refractory  ;  the  heating  efficiency  is  confined  mainly  to  the 
first  portions  of  the  tube  (about  70  %  in  the  first  third) 
as  combination  is  complete  in  a  short  length,  the  granular 
material  in  the  remaining  portion  of  the  tubes  acting  merely 
to  improve  the  turbulence  and  so  increase  the  coefficient  of 
heat-interchange.  It  is  stated  that  the  gases  leave  at 
130-200°  C.,  a  net  thermal  efficiency  of  over  90  % 
being  realized.  Thus,  a  boiler  with  no  3"  tubes  (4'  long) 
erected  at  the  works  of  the  Skinningrove  Iron  Company, 
Ltd.,  gave  an  evaporation  of  14  lbs./hr./ft.2  surface  at  and 
from  100°  C.,  burning  coke-oven  gas,  and  an  efficiency  of 
93  %  °r  94  %  lagge(l.  In  other  cases  an  evaporation  of  20 
lbs./hr./ft.2  is  claimed. 


GASEOUS  FUELS  357 

In  the  later  types  wide  tubes  (about  6")  of  considerably 
greater  length  are  used.  A  specially  moulded  refractory  is 
used  in  the  tubes,  and  combustion  is  not  flameless  as  in  the 
Skinningrove  boiler,  giving  a  longer  life  to  the  refractory. 
The  air-gas  mixture  is  supplied  at  a  pressure  of  about  20  in. 
of  water. 

The  process  works  best  with  gases  of  high  calorific  inten- 
sity, such  as  coal  gas,  carburetted  water  gas,  natural  gas, 
etc.,  but  even  blast  furnace  gas  may  be  used  by  first  starting 
up  with  coke-oven  gas  or  by  using  pre-heated  air.  I^arge 
hardening  furnaces  have  been  constructed  with  a  thermal 
efficiency  of  32  %,  while  claims  are  made  for  the  melting  of 
brass  with  175  ft.3/lb.  (cf.  p.  349),  equivalent  to  a  net  thermal 
efficiency  of  the  order  of  29  %.  I^ead  melting  is  effected  by 
means  of  a  bent  submerged  tube  packed  with  a  granular 
refractory,  with  an  efficiency  of  some  69  %. 

Diaphragms  of  the  type  described  have  found  successful 
application  in  the  evaporation  of  sugar  solutions. 


Gas  Calorimetry 

In  the  control  of  plant  for  the  production  and  utilization 
of  gaseous  fuels,  efficiency  and  economy  are  greatly  enhanced 
by  the  use  of  calorimetric  testing  apparatus,  especially 
recording  apparatus.  The  usual  type  of  gas  calorimeter, 
e.g.  those  of  Junker  and  Boys,  consists  essentially  of  a  central 
combustion  chamber  in  which  the  gas  flame  burns  at  a 
burner  without  touching  the  walls,  the  products  of  combustion 
being  led  through  or  round  coils  or  tubes  in  counter-current 
to  a  regulated  stream  of  cold  water,  the  temperature  rise  in 
which  is  noted  by  means  of  suitable  thermometers.  In  the 
Boys  calorimeter  the  water  content  is  only  about  £  that  of  the 
Junker.  The  thermal  efficiency  exceeds  99  %  under  suitable 
conditions.  The  condensed  water  is  collected  and  the 
necessary  correction  applied  for  the  calculation  of  the  net 
calorific  value — roughly  equivalent  to  a  deduction  of  600 
calories  per  c.c.  water. 

It  is  not  difficult  to  render  such  an  instrument  recording  ; 


358  INDUSTRIAL  GASES 

in  the  Junker  instrument  this  is  accomplished  by  recording 
the  E.M.F.  of  a  differential  thermocouple  measuring  the 
temperature  difference  between  the  inlet  and  exit  water 
streams  respectively,  the  water  and  gas  rates — or  their  ratio — 
being  maintained  constant  by  suitable  means.  The  Sarco 
instrument  depends  on  the  difference  in  the  height  of  two 
columns  of  oil  interconnected  at  the  bottom,  one  of  the 
columns  being  heated  by  the  gas  flame  and  provided  with  a 
jacket  carrying  radiator  fins  ;  net  values  are  indicated. 


REFERENCES  TO  SECTION  XIII. 

Taylor,  "Economic  Fuel  Production  in  Chemical  Industry."  This 
Series.  London,  1919. 

Brame,  "Fuel:  Solid,  Liquid  and  Gaseous."  2nd  Edition.  London, 
1917. 

Bone,  "  Coal  and  its  Scientific  Uses."     London,  1918. 

Meade,  "  Modern  Gasworks  Practice."     London,  1916. 

Thorpe's  "  Dictionary  of  Applied  Chemistry."  London,  1912.  Articles 
on  Fuel  and  Water  Gas. 

Dowson  and  Larter,  "  Producer  Gas."     London,  1906. 

Robson,  "  Power  Gas  Producers,  their  Design  and  Application." 
London,  1908. 

Clerk,  "  The  Gas,  Petrol  and  Oil  Engine,"  New  Edit.     London,  1909. 


INDEX   OF   SUBJECTS 


ABRAHAM-MARMIER  ozone  system, 

144 
water  sterilization  system,  146-7 

Absolute  zero,  7 

Acetates,  synthetic  production  of. 
251 

Adiabatic  compression  of  gases, 
34-8 

Air  producer  gas,  313-16 

Air,  58-92  ;    properties,  58 

Liquid  air,  useful  constants, 
69  ;  manufacture,  69-77  ; 
properties,  77-8 ;  applica- 
tions, 78-9 ;  separation  of 
constituents  of,  79-92 

Air  purification  by  ozone,  148-9 

Alma  producer,  334,  336 

Ammonia  equilibrium,  216 
recovery,  337—40 
-soda  process,  269 
synthesis.     See  Haber  process. 

Argon,  124-8 ;  occurrence,  124 ; 
manufacture,  124-7 ;  pro- 
perties, 127-8  ;  applications, 
127-8 

Arc  process,  107,  121 

Asphyxiating  gases,  291-4 

Atmosphere,  composition  of,  58-9 

Automatic  safety  and  purity  tests, 
33-4 

Avogadro's  hypothesis,  1 

BALLOONS,  223 

B.A.M.A.G.  (Bunte)  hydrogen  pro- 
cess, 192,  194 

continuous  catalytic  hydrogen 
process,  20,  49,  159-64,  173, 
185,  207,  210,  212,  213,  219, 
235,  263,  325 

Barium  peroxide,  dissociation  pres- 
sure of,  97 

Bedford  process  for  the  removal  of 
carbon  dioxide,  173,  210 

Bergius  hydrogen  process,  187-9, 
212 

Blast  furnace,  dry  blast  for,  50-2 
gas,  353-4 


;   Bone-Court  boiler,  356-7 

Boyle's  Law,  2 

Boys'  gas  calorimeter,  357 

Braun  nitrogen  process,  115 
i   Brayshaw  furnace,  351 

Brin  process,  96-7,  112 
I   British     Oxygen     Co.'s     hydrogen 

liquefaction  apparatus,  154 
i   Bucher  process,  94,  120-21 

Burdett   electrolytic    process,    198, 
201 

i   CALCIUM     carbonate,     dissociation 
pressure  of,  260 

Calorific  intensity,  298 

Calorimetry,  gas,  357-8 

Calorific  value,  296,  299 

Carbon  dioxide,  256-73 ;  occur- 
rence, 256  ;  properties,  43-5, 
256-9 ;  dissociation,  257 
Manufacture,  259-69  ;  pure 
carbon  dioxide,  259-63 ; 
utilization  of  natural  sources, 
259-60 ;  thermal  decom- 
position of  carbonates,  260- 
61  ;  action  of  acids  on 
carbonates,  261-2  ;  by-pro- 
duct in  fermentation  pro- 
cesses, 262 ;  concentration 
from  mixtures  with  other 
gases,  209-10,  263-9 
Applications,  269-72  ;  estima- 
tion and  testing,  272-3 ; 
liquid  carbon  dioxide,  258, 
268  ;  solid  carbon  dioxide, 
258-9,  268-9 

Carbon  monoxide,  208,  237-55 ; 
properties,  237-41  ;  decom- 
position of,  237-9 ;  equili- 
brium with  carbon  dioxide 
and  carbon,  14-16,  237-9, 
303;  manufacture,  241-2 
Applications,  242-54 ;  Mond 
nickel  process,  243-8  ;  pro- 
duction of  formates,  oxalates 
and  acetates,  248-51  ;  pro- 
duction of  gases  rich  in 


360 


INDEX  OF  SUBJECTS 


Carbon  monoxide — continued. 

methane,      251-2 ;       manu- 
facture of  phosgene,  252-4  ; 
other  applications,  254 
Estimation,  254-5 

Carbonium  Gesellschaft  hydrogen 
process,  192,  212 

Carbonyl  chloride,  252-4 

Carbonyls,  243-4 

Carburetted  water  gas,  322-5 

Cascade  method  of  liquefying  gases, 
60-61 

Castner-Kellner  electrolytic  process, 
202-3 

Catalysis,  heterogeneous,  17-20 
homogeneous,  17 

Charles'  and  Gay  Lussac's  Law,  2 

Charpentier  ozone  process,  138 

Chemical  constant,  15-16 

Churchill  electrolytic  process,  198, 
201 

Cleaning  of  gases,  "27-9 
semi-water  gas,  337-40 

Claude  hydrogen  system,  165,  170- 

72 

liquid  air  system,  75-7 
oxygen  and  nitrogen  plants,  87- 
90 

Claus  process,  210,  264 

Claus-Chance  sulphur  recovery  pro- 
cess, 269 

Coal  gas  as  a  fuel,  347-52 

Coke-oven  gas,  352-3 

Compressed  gases,  safety  precau- 
tions, 39-45 

Compressibility  of  gases,  2-7 

Compression  of  gases,  34—9 

Conversion  factors,  56 

Cottrell  precipitator,  28-9 

Critical  pressure,  10 
temperature,  10 

Crossley  ammonia  recovery  plant, 

340 
fan  extractor,  344 

Cutting  of  metals  with  oxygen, 
104-5 

Cyanamide,  85-6,  94,  118-19,  121, 
125 

Cyanide  process  (Nitrogen  fixation). 
See  Bucher  process. 

Cylinders,  gas,  39,  41-5 ;  Parlia- 
mentary Committee  on  the 
manufacture  of,  39,  44,  45; 
maximum  charges  of  lique- 
fied gases,  42-5,  268,  280 

D  ALTON'S  Law,  2,  8 
Dellwik-Fleischer  water  gas  plants, 
319,  320-21 


Density  of  gases,  25-6 

Dieffenbach       and       Moldenhauer 

hydrogen  process,  185-6 
I   Diffusion,  9-10 
|  Dowson  producer,  343 
i  Drying  of  gases,  50-52 
!  Duff  producer,  335 

Duff-Whitfield  producer,  343 

EDISON  effect,  128 

Effusion,  26 

Electrolysis  of  water,  constants, 
195 

Electrolytic  hydrogen,  194-203 

Electrostatic  separation  of  im- 
purities from  gases,  28 

"  Epurite,"  99 

Equilibrium,  14 

Exhaled  air,  composition  of,  59 

Explosion,  velocity  of  propagation 
of,  300-01 

Explosive  limits,  40,  202,  297,  300 

FAT    hardening.     See    Hydrogena- 

tion  of  oils  and  fats. 
Formates,  synthetic  production  of, 

205,  208,  271-2 

Fuels,  classification  of  solid,  326-7 
Furnaces,  use  of  semi-water  gas  in, 

340-41  ;    use  of  coal  gas  in, 

348-51 

'  GAILLARD  tower,  28 
Gas  analysis,  33-4,  56 

cylinders.     See  Cylinders,  Gas. 
holders,  52 

Gaseous  fuels,  fundamental  prin- 
ciples relating  to  use  of, 
296-301  ;  composition  of, 
297  ;  fundamental  principles 
of  production  of,  301-13 
Air  producer  gas,  313-18 
Blue  water  gas,  318-22,  325  ; 
Lowe  system,  319  -  20  ; 
Dellwik  -  Fleischer  system, 
320-21  ;  Kramer  and  Aarts 
process,  321-2 

Carburetted  water  gas,  322-5 
Semi-water  gas,  325-47  ;  choice 
of  fuel,  326-8 ;  saturation 
temperature  of  blast,  328- 
34;  Bone  and  Wheeler's 
experiments,  329-32 ;  rate 
of  gasification,  334  -  5  ; 
pressure  plants,  335-7 ; 
ammonia  recovery  and  clean- 
ing, 337-40  (Mond  process, 
339-40) ;  use  for  furnace 


INDEX  OF  SUBJECTS 


361 


Gaseous  fuels — continued. 

Semi-water  gas — continued. 
operations,  340-41  ;  pro- 
duction of  power  from, 
341-2 ;  plants  for  power 
generation,  343-4 ;  suction 
plants,  344-7 

Coal  gas  as  a  fuel,  347-52  ; 
coke-oven  gas,  352-3  ;  blast- 
furnace gas,  353-4  ;  natural 
gas,  354-5 ;  surface  com- 
bustion, 355-7  ;  gas  calori- 
metry,  357-8 

Gases,  tables  of  properties  of,  53-6 

Gasification  in  producers,   rate  of, 
334-5 

Garuti    electrolytic    process,     198, 
199-200,  202 

Gay  Lussac's  Law,  2 

General  Electric  Co.'s  ozone  pro- 
cess, 144 

Gerard,  ozone  system,  145 

water  sterilization  system,  147 

Griesheim-Elektron     field     process 

for  hydrogen,  231 
hydrogen    process,     156,     164-8, 
170,  186 

HABER  process,  94,  119,  121,  213, 

215-20 

Half-watt  lamp,  122,  128 
Hampson  system  of  air  liquefaction, 

69-70 
Hanisch     and     Schroder     sulphur 

dioxide    process,    275,    276, 

277,  278-9 

Harcourt  nitrogen  process,  113 
Hargreaves  process,  280 
Hausser  process,   107-8,  121 
Heat-interchange,  45-50,  57 
Heat  of  combustion,  13 
Helium,  130-32 
Henry's  Law,  8,  256 
Hermansen  furnace,  350 
High  pressure  gas,  350-51 
Hildebrandt  oxygen  and  nitrogen 

plants,  91-2 

Hot-wire  anemometry,  32-3 
Howard-Bridge  ozone  system,  144 

water  sterilization  system,  147 
Humphreys  and  Glasgow  water  gas 

plant,  322-5 

Hydrogen,         152-236 ;          Joule- 
Thomson   effect   in,    67  -  8  ; 

occurrence,  152  ;    properties, 

3,  152-5 
Manufacture,  stationary  plants, 

155-207 ;     from   water   gas, 

replacement  of  carbon  mon- 


Hydrogen — continued. 

Manufacture — continued. 

oxide  by  hydrogen,  156- 
68 ;  from  water  gas  by 
liquefaction  of  the  carbon 
monoxide,  168-74 ;  by  the 
action  of  water  or  steam  on 
iron  or  carbon,  174-89  (Iron 
oxide  processes,  175-85 ; 
Lane  process,  178-82 ; 
Messerschmitt  process,  182- 
4  ;  other  processes,  184-5  ; 
Dieffenbach  and  Molden- 
hauer  process,  185  -  6  ; 
Bergius  process,  187-9) ;  by 
decomposition  of  hydro- 
carbons, 189-94  (Carbonium 
Gesellschaft  process,  192  ; 
Rincker  and  Wolter  process, 
192-3 ;  Oechelhauser  pro- 
cess, 193-4 ;  B.A.M.A.G. 
process,  194) ;  by  electro- 
lysis, 94-5,  194-203  ;  other 
processes,  203-7 ;  produc- 
tion of  a  mixture  of  nitrogen 
and  hydrogen,  207 

Purification,  207-13 ;  from 
carbon  monoxide,  208-9 ; 
from  carbon  dioxide,  209-10  ; 
from  sulphur  compounds, 
210-11  ;  from  other  im- 
purities, 211-12 

Cost  and  purity  of,  212-13,  234 

Applications,  213-21  ;    hydro- 

fenation  of  oils  and  fats, 
14-15 ;  manufacture  of 
synthetic  ammonia,  215-20  ; 
other  applications,  221 
Manufacture  in  the  field,  223- 
34  ;  portable  apparatus,  224- 
32 ;  Silicon  and  Silicol 
processes,  224  -  7  ;  Hydro  - 
genite  process,  227-8 ; 
Hydrolith  process,  228-9  ; 
by  action  of  acids  and  alkalis 
on  metals,  229-31  ;  other 
processes,  231  -  2  ;  semi  - 
portable  plant,  232  -  3  ; 
stationary  plants,  233  ;  lift- 
ing power,  234 ;  effect  on 
fabrics,  234;  costs,  234. 
Testing  of,  235-6 

Hydrogenation    of    oils    and    fats, 
214-15 

Hydrogenite  process,  98,  227-8 

Hydrolith  process,  228-9 

IGNITION  temperature,  299-300 
Interferometer,  gas,  25 


362 


INDEX  OF  SUBJECTS 


International  Oxygen  Co.'s  electro- 
lytic process,  198,  200-01 
Internationale     Wasserstoff     A.G. 
hydrogen  process,  178,  184-5 
Iron  carbonyls,  244 

oxides,  equilibria  in  reduction  by 

hydrogen,  175 

oxide  processes  for  hydrogen, 
175-85 

JOULE-THOMSON  effect,  10-11,  61-8, 

154,  170 
Joule's  Law,  11 
Junker  gas  calorimeter,  357 

KERPELY  producer,  336,  337 
Kerpely-Marischka  producer,  336 
Kitzinger  nitrogen  process,  115 
Kramer  and  Aarts  water  gas  plants, 

321-2 
Krypton,  132 

LANE  hydrogen  process,  168,  178- 
82,  184,  213 

Latent  heats  of  fusion  and  evapora- 
tion, 13 

Level,  influence  of  difference  in, 
24-5 

Lifting  power  of  hydrogen,  233-4 ; 
of  helium,  234 

Linde  oxygen  and  nitrogen  plants, 

81-7 

system  of  air  liquefaction,  73-4  ; 
theory  of,  61-8,  70-72 ; 
effect  of  pre-cooling  in,  72—3 

Linde-Frank-Caro  process,  50,  116, 
172-4,  204,  210,  212,  215, 
219,  222,  233,  242,  251,  263 

Liquefaction  of  permanent  gases, 
60-92 ;  theory  of  Joule- 
Thomson  effect,  61-8 

Liquefied  gases,  42-5 

Liquid  air,     See  Air. 
hydrogen,  154 

Livesey  tar  separator,  344 

Lymn  ammonia  recovery  plant, 
340 

MAURICHEAU-BEAUPRE  process,  231 

Measurement  of  rate  of  flow,  29-33 

Melsens-Pictet  sulphur  dioxide  pro- 
cess, 276 

Messerschmitt  hydrogen  process, 
178,  182-4 

Meters,  gas,  29 

Methane  equilibrium,  189 

production  from  carbon  monoxide, 
209,  240-41,  251-2 

Mine  rescue  apparatus,  78-9 


Mineral  waters  (artificial),  269-70 
Mond  gas,  339-40 

nickel  process,  242,  243-8 

producer,  334,  335,  336 
Moore  lamp,  129 

producer,  338-9 

NATURAL  gas,  354-5 

Neon,  128-30 

Nernst  Heat  Theorem,  14-16,  135, 
216,  240,  253,  285 

Nickel  carbonyl,  241,  243-4 

Niton,  132-3 

Nitrogen,  110-22;    properties,  110, 

111 

Manufacture,  79-92,  111-16; 
by  the  fractionation  of  liquid 
air,  79,  92,  112;  by  direct 
chemical  removal  of  the 
oxygen  from  air,  112-14 ; 
from  producer  gas  and  pro- 
ducts of  combustion,  114-15 ; 
by  physical  methods  (in  the 
gaseous  state),  115-16  ;  by 
direct  chemical  methods, 
116 

Purification,  116-17  ;  cost  and 
purity,  117 ;  applications 
(nitrogen  fixation),  117-22  ; 
estimation  and  testing,  122 

Nitrogen  content  of  coal,  327-8 
fixation,  117-21 

Nitrous  oxide,  285-90  ;  properties, 
43-5,  285-6 ;  manufacture, 
286-8 ;  purification,  288  ; 
applications,  288-90 

•  OECHELHAUSER   hydrogen   process, 

192,  193-4 

i   Orifice  meters,  29,  30 
Ostwald  process,  108,  121    - 
Otto  ozone  system,  144 
water  sterilization   system,    147, 

148 
Oxalates,  synthetic  production  of. 

See  Formates. 
|  Oxygen,  93-109  ;    properties,  93 

Manufacture,  79-92,  94-100 ; 
by  the  fractionation  of  liquid 
air,  79-92,  94  ;  by  electro- 
lysis, 94-5,  194-203 ;  by 
alternate  formation  and  de- 
composition of  higher  oxides, 
etc.,  95-8 ;  by  auto-com- 
bustion methods,  98  ;  by  the 
action  of  water  on  peroxides 
and  the  like,  98-9;  by 
physical  methods  (in  the 
gaseous  state),  99-100 


INDEX  OF  SUBJECTS 


363 


Oxygen — continued. 

Compression,  42,  100-01  ;  cost 
and  purity,  101-2  ;    applica- 
tions,     102-8 ;      estimation 
and  testing,  108-9 
Oxygen-enriched  air,  106-8 
Oxygenite,  98 
Oxylithe,  99 
Ozonair    air    purification    system, 

148-9 

ozone  system,  144 
water  sterilization  system,  147 
Ozone,    134-51  ;    occurrence,    134 ; 

properties,  134-36 
Production,  136  -  40  ;  by 
chemical  methods,  137  ;  by 
thermal  treatment  of  oxygen, 
137-8  ;  by  electrolysis,  138- 
9  ;  by  photochemical  means, 
139 ;  by  the  electric  dis- 
charge, 139-40 

Manufacture,  general  principles 
of  ozonizers,  140-43 ;  com- 
mercial ozonizers,  143-5 
Applications,  145-51  ;  water 
sterilization,  145  -  8  ;  air 
purification,  148-9 ;  chemi- 
cal applications,  149 

PELOUZE    and    Audouin    tar    ex- 
tractor, 344 
Permeability    of    materials,    9-10, 

153-4 

Phosgene,  252-4 
Physical  constants,  53-7 
methods    of    testing    purity    of 

gases,  25-6 
Pictet  oxygen  and  nitrogen  plants, 

90-91 

Pitot  tube,  30-32 
Plumboxan  process,  96 
Poison  gases,  291-4 
Power  production,  from  semi-water 

gas,  341-2 

producer  plant  for,  343-4 
suction  plants  for,  344-7 
from  coal  gas,  351-2 
Properties  of  gas,  tables  of,  53-6 

RARE  gases  of  the  atmosphere,  92, 
123-33  ;  discovery  of,  123-4 

Reaction  velocity,  17 

Reference  data,  53-6 

Resistance  to  flow  of  gases,  22-4 

Richmond  Gas  Stove  Co.'s  furnace, 
351 

Rincker  and  Wolter  hydrogen 
process,  192-3 

Ruston  suction  gas  plants,  346 


SAFETY     precautions     with     com- 
pressed gases,  39—45 

Sarco  carbon  dioxide  apparatus,  33 
gas  calorimeter,  358 

Saturation  temperature  of  air  blast, 
328-34 

Schmidt  electrolytic  process,    198, 
199 

Schoop    electrolytic    process,    198, 
200 

Schriver   electrolytic   process,    198, 
201 

Schuckert  electrolytic  process,   95, 

198,  202 

(Silicon)  hydrogen  process,   224, 
225 

Semi- water  gas.     See  Gaseous  fuels. 

Separation    of    gaseous    mixtures, 

26-7,  79-81 

liquid    or    solid    particles    from 
gases,  27-9 

Serpek  process,  119-20 

Siemens  and  Halske  ozone  system, 

143-4,  147 
water  sterilization  system,  146-7 

Silicol  hydrogen  process,  225-7,  235 

Siemens  de  Frise  water  sterilization 
system,  147 

Smith  Gas  Corporation's  tar  separa- 
tor, 344 
suction  gas  plant,  345 

Solubility  of  gases,  8 

Solvay  process,  269 

Sorption,  8-9 

Space- velocity,  18 

Space- time-yield,  18 

Specific  heats  of  gases,  11—13 

Storage  of  gas,  52 

Strache  hydrogen  process,  185 

Stream-line  motion,  20-22 

Suction  gas,  344-7 

Sulphur  dioxide,  274-84  ;  proper- 
ties, 43-5,  274-5 
Manufacture,  275-80 ;  pro- 
duction of  dilute  sulphur 
dioxide,  277-8  ;  concentra- 
tion of  dilute  sulphur  dioxide, 
278-9 

Applications,  280-83  ;  estima- 
tion and  testing,  283-4 ; 
liquid  sulphur  dioxide,  279- 
80 

Sulphur  content  of  coal,  328 

Surface  combustion,  355-7 
friction,  23 

Siirth  carbon  dioxide  process,  266-7 

THEISSEN  fan,  354 
Thermochemistry,  13-14 


INDEX   OF  SUBJECTS 


Tindal  water  sterilization  system,  147 
Tindal  de  Frise  ozone  system,  144 
Turbulent  motion,  20-22 

VENTURI  meter,  30 
Verley  vanillin  process,  149 
Viscosity  of  gases,  20-21 
Vosmaer  ozone  system,  144 
water  sterilization  system,  147 


WATER  gas,  blue,  156,  316-22,  325 

carburetted,  322-5 

equilibrium,  157-8,  238-9,  309 
Water  sterilization  by  ozone,  145-8 
Welding  autogenous,  103-4 
Wood  pulp  manufacture,  280-81 


ZENON, 132 


INDEX   OF   NAMES   OF  AUTHORS 


ALDER,  113 

Amagat,  3,  43,  258 

American  Air  Nitrates  Corporation, 

119 
American  Cyanamide  Co.,  113,  119, 

125 

American  Oxhydric  Co.,  200 
Anderson,  227 
Andrew,  250 
Archibald,  139 
Ardol,  Ltd.,  172 
Artigue,  99 
Ashcroft,  232 
Athion  Gesellschaft,  242 
Austin,  58,  93 
Auld,  292 
Avogadro,  1 

BADISCHE  ANILIN  &  SODA  FABRIK, 
120,  156,  158,  159,  161,  162,  168, 
170,  176,  177,  191,  205,  208,  211, 
217,  218,  220,  263,  264 

Baggs,  175,  209 

Baillio,  225 

Ball,  263 

Baly,  79,  80 

Bamberger,  228 

Barlow,  196 

Barnitz,  182,  222 

Bartelt,  100 

Barton,  204 

Baskerville,  289 

Basset,  276,  277 

Baur,  181  • 

Bayer  &  Co.,  218 

Becquefort,  204 

Bedford,  211 

Behrens,  262 

Beill,  143 

Bendixsohn,  138 

Benier,  344 

Benjamin,  242 

Bergfeld,  98 

Bergius,  187 

Bergmann,  276 

Berlin  Anhaltische  Maschinenbau 
A.  G.  (B.A.M.A.G.),  161,  184, 
191,  192 


Berliner,  276 

Bernthsen,  222 

Berry,  354 

Berthelot,  143,  248 

Bischof,  313 

Binder,  109 

Bjerrum,  257 

Blagburn,  112 

Blum,  198,  222 

Bock,  256 

Bock,  228 

Bodenstein,  18,  19,  126 

Bohr,  256 

Bone,   19,  315,  320,  322,  329,  334, 

337,    338,   341,    347,    355,    356, 

358 

Bornstein,  57 
Bosch,  191,  220 
Boudouard,  16,  238,  303 
Bourchaud,  229 
Boussingault,  96 
Boyer,  236 
Bradley,  64,  65 
Brahmer,  138,  221 
Brame,  347,  358 
Bramkamp,  77 
Bredig,  249,  272 
Brianchon,  95 
Brindley,  231 
Briner,  140,  238 
Erin's  Oxygen  Co.,  96,  97 
Briscoe,  133 
British  Oxygen  Co.,  69,  70,  84,  95, 

97,  198 
Brodie,  136 
Brook,  349 
Brownlee,  115,  192 
Brunei,  274 
Buchanan,  160 
Bucher,  113,  120,  125 
Buffa,  200 
Bulle,  57 
Bunte,      192,      309,       316,      318, 

336 

Burdett,  197 
Burrell,  40,  202,  355 
Bush,  29 
Byk,  99 


366 


INDEX  OF  NAMES   OF  AUTHORS 


CAILLETET,  60 

Callendar,  298 

Calvert,  20 

Campari,  286 

Campbell,  326 

Carbonium  Gesellschaft,  192 

Cardoso,  57 

Caro,  115,  118 

Carpenter,  C.,  211 

Carpenter,  H.  C.  H.,  181 

Carpenter,  C.  W.,  40 

Carrol,  261 

Carter,  249,  272 

Carulla,  204 

Castner-Kellner,  203 

Cavendish,  124 

Cedford  Gas  Producing  Co.,  251 

Centrallstelle  fur  wissenschaftlich- 

technische  Untersuchungen,  218 
Chaillaux,  98,  206 
Chance,  354 
Chapman,  135 
Charles,  2 
Chaudron,  175 
Chemische  Fabrik  Griesheim-Elek- 

tron,  126,  158,  164,  203,  231 
Chemische    Fabrik    von    Heyden, 

A.  G.,  204 
Chemische    Fabrik    vorm.    Moritz, 

Milch  &  Co.,  187 
Churchill,  197 
Chwolson,  56 
Clamond,  204 
Claude,  68,  81,  92,   126,   128,   129, 

170,  210 
Glaus,  210 
Clayton,  215  ^ 
Clement,  138 
Clerk,  358 
Coehn,  95 
Collie,  129 
Colton,  288 

Companie  du  Gaz  de  Lyons,  159 
Consortium    fur    Elektrochemische 

Industrie,  G.m.b.H.,  224 
Cottrell,  28,  130,  132 
Cowap,  244 

Coward,  40,  241,  299,  300 
Cowper-Cowles,  197 
Crofts,  57,  110,  152,  257 
Crookes,  208 
Crossley,  122,  222 
Cyanidgesellschaft,  112 

DALTON,  2 
Dammer,  199 
D'Arsonval,  196,  204 
Davy,  286,  355 
Deguide,  204 


De  Jahn,  218 

Dellwik,  320 

Dellwik  -  Fleischer     Wassergas 
G.m.b.H.,  176 

Dempster,  177,  178 

Dendy,  271 

Denis,  250 

De  Villepique,  100 

Dewar,  10,  79,  102,  127,  128,  129, 
132,  153,  154 

Dieffenbach,  176,  185,  180,  190,  207 

Dixon,  299,  300,  301 

Don,  151 

Dorn,  131 

Dowson,  344,  358 
j    Dreaper,  115 
I    Dubox,  250 

Durand,  140 

Dykema,  355 

EASTWICK,  204 

Eberlein,  277 

Edgar,  153 

Egloff,  355 

Elektrizitats,  A.  G.,  vorm.  Sclmckert 

&  Co.,  197 

Elektrizitatswerk  Lonza  A.  G.,  113 
Elektrochemische  Werke,  Bitterfeld, 

249,  251 

Elkan  Erben,  G.m.b.H.,  231 
Ellis,  115,  192,  193,  215,  221,  250 
Elmore,  287 
Elworthy,  114,  204 
Enderli,  272 
Engelhardt,  109,  222 
Engels,  165 
Erdmann,  215,  251 
Erlwein,  141,  142,  151 
Escher,  57 
Evans,  211 
Eycken,  197 

FALK,  300 

Farbwerke  vorm.  Meister,  Lucius  & 

Briining,  106,  113 
Fay,  239 
Feldkamp,  205 
Ferguson,  G.  E.,  239 
Ferguson,  J.  B.,  274 
Fielding,  229 
Filippo,  126,  128 
Fink,  18 
Finke,  112 
Firth,  153 

Fischer,  F.,  125,  138,  139,  202 
Fischer,  H.,  258 
Flagg,  286 
Fletcher,  104 
Foersterling,  99,  231 


INDEX  OF  NAMES  OF  AUTHORS 


367 


Fonda,  126,  248 
Fonrobert,  150 
Forshaw,  241 
Forster,  349 
Fournier,  100 
Fourniols,  236 
Frank,  115,  118,  209 
Franke,  112 
Frankland,  222 

GARNER,  92 

Garners  and  Metals  Research  Co., 

276 

Garuti,  196,  197 
Gas  Developments,  Ltd.,  181 
Gas  Light  and  Coke  Co.,  324 
Gauger,  40,  202 
Gautier,  59,  152,  205 
Gay  Lussac,  2 
Gay  ley,  51 
Geeraerd,  197 
General  Chemical  Co.,  220 
General  Electric  Co.,  144 
Gerard,  145 
Gerhartz,  176 
Gesellschaft    fur    Linde's    Eismas- 

chinen,  A.G.      See  Linde. 
Giffard,  176 
Glassner,  181 
Goldschmidt,  249,  250 
Goldstein,  140 
Goosmann,  262,  265,  273 
Graham,  J.,  153 
Graham,  J.  I.,  254 
Gray,  141 
Greenwood,  34,  108,  217,  218,    222, 

350 
Griesheim  -  Elektron      Co.         See 

Chemische     Fabrik     Griesheim- 

Elektron. 
Grillo,  278 
Grouven,  260 
Guillet,  211 
Gutbier,  153 
Gutzeit,  235 
Gwosdz,  309,  310 

HABER,  25,  26,  56,  215,  216,    217, 

218,  222,  249,  309 
Hacker,  344 
Haddon,  112 
Hadfield,  341,  351 
Hahn,  309 
Hahnel,  125 
Hale,  64,  65 
Haller,  284 
Hamburger,  128 
Hampson,  61 
Hanisch,  275 


Hanmann,  99 

Harger,  98,  115 

Harpf,  284 

Harpster,  25 

Harries,  309,  316,  317,  318 

Harries,  C.,  136,  150 

Hart,  276 

Hartley,  349 

Hausbrand,  50,  57 

Hawkins,  229 

Helmholtz,  298 

Helouis,  100,  205 

Hembert,  159 

Henderson,  222 

Henning,  110,  257 

Henry,  8,  159,  239 

Heraeus,  198 

Herman,  355 

Heuse,  57 

Hildebrand,  97 

Hillebrand,  124 

Killer,  210 

Hird,  283 

Hirtz,  244 

Hocking,  348 

Hofmann,  155,  235,  255 

Holborn,  12,  58,  93,  110,  257 

Hollandsche      Residugas  -  Maats- 

chaapij,  192 
Holt,  153 
Hooton,  206 
Horak,  253 
Howard,  262 
Hubert,  353 
Humphrey,  100 

Humphreys  &  Glasgow,  178,  322 
Hunter,  285 
Huntingdon,  A.  K.,  208 
Huntingdon,  T.,  277 
Hutchinson,  354 
Hutin,  205,  277 
Hutton,  113,  242,  350 

INTERNATIONAL  CHEMICAL  Co.,  224 
International  Oxygen  Co.,  105,  199 
Internationale  Wasserstoif  A.G., 

184 
Ipatiew,  214 

JACOB,  175 

Jakob,  12,  58 

Jaubert,  98,  99,  178,  224,  225,  227, 

228 

Jenks,  328 
Johnson,  J.  E.,  107 
Johnson,  J.,  167,  260 
Jones,  135 
Josse,  50 
Jost,  216 


368 


INDEX  OF  NAMES   OF  AUTHORS 


oule,  10,  11 
ouve,  205 
ungfleisch,  274 
unker,  13 

urisch,  9        \ 

KALTENBACH,  277 

Kainmerlingh  Onnes,  61,  131 

Kastner,  96 

Katz,  250 

Kausch,  92,  273 

Kaye,  57 

Kayser,  130 

Keable,  322 

Kendall,  206 

Kershaw,  353 

Kistiakowsky,  127 

Knecht,  113 

Knowles,  197 

Koepp  &  Co.,  249,  250 

Kolbe,  272 

Krupp,  186,  271 

Kubierschky,  100 

LABY,  57 

Ladenburg,  135 

Lahousse,  206 

Lance,  114 

Landin,  210 

Landis,  122 

Landolt,  57 

Lane,  176,  209,  263 

Lange,  275 

Langen,  15 

Langer,  159,  243 

Langmuir,  129 

Larter,  358 

Latchinoff,  196 

Le  Chatelier,  301 

Lehmann,  221 

Leithauser,  140,  142 

Leiser,  26 

Lepsius,   167,    193,    194,    198,    203, 

221 

Le  Rossignol,  216,  222 
Leroy,  197 
Leslie,  264 
Lessing,  190,  241 
Levi,  166 
Levin,  197 
Levy,  100 
Levy,  254 

Lewes,  176,  319,  320,  323 
Lidoff,  287 
Linde,  61,  79,  81,  92,  126,  168,  169, 

170,  208 

Linder,  142,  143 
Lloyd,  283 
Loiseau,  241 


Lorenz,  199 

Lowe,  25 

Lowe,  316 

Lowry,  111 

Lucke,  346 

Luggin,  309,  316 

Luhmann,  265 

Lunden,  178 

Lunge,  34,  56,  222,  273,  275,  284 

Lussana,  12 

Luttinger,  250 

M' ARTHUR,  354 

McBain,  8 

McCourt,  115,  355 

McDavid,  299,  300 

McElroy,  250 

Machalske,  253 

Mackey,  261 

Machtolf,  190,  192 

Majert,  232 

Malaquin,  137 

Malisoff,  355 

Mallard,  301 

Mallet,  95,  100 

Maquenne,  124 

Marechal,  96,  186 

Marengo,  204,  229  " 

Markgraf,  316 

Marselli,  119 

Marston,  113,  287 

Martin,  57,  87 

Marx,  138 

Maschinenbau-Anstalt     Humboldt, 

170 

Maschinenfabrik  Oerlikon,  197,  199 
Maschke,  222 
Massenez,  139 
Matignon,  220 
Matter,  287 

Mauricheau-Beaupre,  231    - 
Maxted,    90,    160,    177,    181,    217, 

222,  241 
Mazza,  100,  204 
Meade,  318,    319,    323,    324,    348, 

358 

Menne,  104 
Mercia,  250 
Merriman,  237 
Merz,  165 

Messerschmitt,  177,  207 
Mewes,  77,  89,  92 
Miethe,  221 
Mills,  337 
Mitchell,  270 
Moldenhauer,    176,    185,    186     190 

207 

Molinari,  57,  278 
Moller,  28 


INDEX  OF  NAMES  OF  AUTHORS 


369 


Mond,  A.,  28 

Mond,  L.,  153,  150,  243,  244,  245 

Moore,  276 

Moritz,  197 

Morris,  32 

Moser,  255 

Motay,  Tessie  du,  90,  104,  180 

Moulin,  270 

Muller,  159 

Murray,  85,  90,  97,  105,  109 

NAEF,  116 

Naher,  159 

Nauss,  190 

Neave,  100 

Nernst,  14,  56,  137,  257 

Neumann,  G.,  153 

Neumann,  K,  329 

New  York  Nitrogen  Co.,  112,  200 

Newbiggin,  22 

Nitridfabrik  G.m.b.H.,  249 

Norman,  214 

Norsk  Hydro  Elektrisk   Kvaelstof- 

aktieselskab,  125 
Norton,  122,  222 
Nussow,  205 

OBACH, 196 

Oehlom,  222 

Oerlikon  Co.     See  Maschinenfabrik 

Oerlikon. 
Ohlmer,  19 
Olszewski,  61 
Onnes,  61,  131 
Orange,  129 
Ovitz,  250 
Ozouf,  265 

PAAL,  214,  235 

Pannell,  22,  23,  24,  30,  32 

Paquiet,  221 

Parkinson,  79,  80,  96,  108 

Parsons,  121,  220 

Partington,  108,  222 

Paterno,  253 

Patterson,  12£ 

Payman,  40 

Perkin,  151 

Perl,  113 

Pernell,  277 

Petavel,  113,  242 

Philip,  99,  231 

Pictet,  43,  60,  105,  191,  282,  288 

Pintsch,  210 

Piva,  166 

Plenz,  40 

Pompili,  196,  197 

Ponnaz,  222 

Porter,  40 

Power  Gas  Cprporation,  339 

A. 


Praceiq,  229 
Prager,  175 
Pratis,  204,  229 
Price,  112 
Pring,  134,  139 
Pryor,  200 
Pullman,  204,  263 

RABENALT,  210 

Ramsay,   123,   124    128,    130,    132, 

133,  153,  270 
Ransford,  99 
Rao,  150 
Rasch,  42,  290 
Rayleigh,  59,  123,  124,  152 
Read,  159 

Regnault,  43,  258,  285 
Reinhardt,  354 
Reissig,  210 
Renard,  196,  211,  230 
Rhead,  9,  238,  303 
Ricarde-Seaver,  208 
Richardson,  D.,  109 
Richardson,  L.  B.,  9 
Richter,  232 
Rideal,  E.  K.,  151,  255 
Rideal,  S.,  151 
Ridsdale,  177 
Rieche,  205 
Riedel,  115 
Rincker,  190,  192 
Ringe,  125 
Robertson,  40,  355 
Robson,  368 
Roscoe,  57 
!    Rose-Innes,  11 
Roth,  57 
Rowley,  344 
Runge,  100 

SABATIER,  155,  158,  214,  240,  258 

Sander,  174,  185,  192,  222,  236 

Sarason,  231 

Scheel,  57 

Schering,  149 

Schmalotta,  265 

Schmid,  255 

Schmidt,  O.,  196,  199 

Schmidt,  R.,  132 

Schmidt,  Rudolf,  272 

Schneider,  155 

Schonbein,  136 

Scholl,  207 

Schoonenberg    &    Naamloze    Ven- 

nootschap    Philips    Metal    Gloe- 

lamp-fabrik,  126 
Schoop,  197 
Schorlemmer,  57 
Schriver,  198,  199,  201 

24 


370 


INDEX  OF  NAMES   OF  AUTHORS 


Schroder,  275 

Schuck,  214 

Schuckert.     See  Elektrizitats  A.G. 

vorm.  Schuckert  &  Co. 
Schwarz,  232 
Seeker,  239 

Selby  Smelter  Commission,  275 

Senderens,  168,  214,  240,  258 

Seyler,  327 

Shenton,  100 

Shields,  153 

Siebert,  25 

Siemens,  61,  68,  139,  196,  206 

Sieverts,  122 

Simmersbach,  353 

Simpson,  277 

Sinding-Larsen,  98 

Skita,  214 

Smith,  C.  C.,  181 

Smith,  R.  F.  W.,  328 

Smith,  R.  H.,  258,  259 

Smith,  W.,  287 

Smythe,  275 

Snelling,  205 

Soc.  Anon.  1'Oxhydrique  Fran9aise, 
197 

Soc.     Anon.    1'Oxhydrique    Inter- 
nationale, 104 

Societe    Christiania    Minekompani , 
220 

Societe  Fran$aise  1'Oxylithe,  226 

Societe  Generate  des  Nitrures,  120 

Societe  1'Air  Liquide,  165,  170 

Soddy,  130 

Sodermann,  288 

Soret,  136 

South  Metropolitan  Gas  Co.,  211 

Soyer,  227,  235 

Spence,  113 

Spencer,  112 

Squire,  94 

Stanton,  22,  23,  24,  32,  47 

Steere,  344 

Stern,  190 

Stevenson,  289 

Stewart,  44,  268,  273 

Steynis,  143 

St.  John,  190 

Stopes,  326 

Storm,  98 

Strache,  185,  210 

Streintz,  153 

Stromeyer,  250 

Strutt,  111 

Stuckert,  272 

Summers,  122 

TAMARU,  222 
Tavlor,  255,  358 


Teichmann,  43,  44,  284 
Teisen,  350 
Teissier,  98,  206 
I  Tellier,  220 
Terres,  40,  336 
Thorn,  260 
Thomas,  32 
Thompson,  136 
Thomson,  10 
Thornton,  349 
Thorpe,  57,  101,  270,  273,  315,  329, 

358 

Thorssell,  178 
Tookey,  347 
Torley,  287 
Trasenster,  107 
Travers,  56,  92 
Tripler,  61 

UHLINGER,  115,  192 
United  Alkali  Co.,  249 
Usher,  150 
Uyeno,  231 

VALENTIER,  132 

Valon,  106 

Van  der  Waals,  7 

Vandoni,  276 

Van  Marum,  136 

Verley,  149 

Verneuil,  221 

Vignon,  160,  318 

Villard,  43,  285,  288 

Voigt,  332 

Von  Wartenberg,  139,  257,  274 

Vosmaer,  141,  148,  150 

WACHEMHEIM,  126 
Wallace,  263 
Walter,  350 
Wanz,  228 
Warburg,  140,  142 
Wardlaw,  275 
Washburn,  122,  125 
Waygouny,  272 
Weber,  F.  A.,  248 
Weber,  S.,  57 
Weinland,  109 
Weise,  205 
Weiskopf,  265 
Weith,  166 
Wells,  288 
Welton,  112 
Wendt,  314,  334 
Wentzki,  211 
Werder,  273 
Westman,  260 
Westinghouse  Co.,  145 


INDEX  OF  NAMES   OF  AUTHORS. 


Wheeler,  9,  10,  238,  303,  320,  32'.), 

334,  337,  338,  347 
White,  A.  H.,  344 
White,  S.,  94 
Wild,  221 

Williams,  C.  E.,  211 
Williams,  F.  M.,  281 
Williams,  T.,  208 
Willstatter,  214 
Windhausen,  264 
Wirth,  344 
Wise,  113 

Witkowski,  6,  58,  65 
Wohler,  41,  78,  175 


Wolf,  M.,  202 
Wolf,  R.  B.,  276 
Wolter,  190,  192 
Woltereck,  237 
Wood,  328 
Worsley,  250 
Wright,  26 
Wr6blewski,  61,  256 
Wroczynski,  238,  286 
Wiirth,  315 

ZEALLEY,  34,  108 
Zeleny,  258,  259 
Ziegenberg,  151 


THE  END 


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